String.Format 方法

定义

重载

示例

调用方法的多 Format 个示例贯穿本文的 " 备注 " 部分。Numerous examples that call the Format method are interspersed through the Remarks section of this article.

你还可以下载一组完整的 String.Format 示例，其中包括 适用于 c # 的 .net Core 项目。You can also download a complete set of String.Format examples, which are included a .NET Core project for C#.

下面是本文中包含的一些示例：The following are some of the examples included in the article:

创建格式字符串Create a format string

插入字符串Inserting a string
格式项The format item
设置具有相同索引的项的格式Format items that have the same index

控制格式化输出Control formatted output

控制格式设置Controlling formatting
控制间距Controlling spacing
控制对齐方式Controlling alignment
控制整数位数Controlling the number of integral digits
控制小数点分隔符后的位数Controlling the number of digits after the decimal separator
在结果字符串中包含字面大括号Including literal braces in a result string

使格式字符串区分区域性Make format strings culture-sensitive

区分区域性的格式设置Culture-sensitive formatting

自定义格式设置操作Customize the formatting operation

自定义格式设置操作A custom formatting operation
截距提供程序和罗马数字格式化程序An intercept provider and Roman numeral formatter

注解

本节内容：In this section:

开始处理字符串. 格式方法Get started with the String.Format method
我要调用哪种方法？Which method do I call?
Format 方法 briefThe Format method in brief
格式项The Format item
如何设置参数的格式How arguments are formatted
设置具有相同索引的项的格式Format items that have the same index
格式设置和区域性Formatting and culture
自定义格式设置操作Custom formatting operations
字符串格式 Q &String.Format Q & A

开始处理字符串. 格式方法Get started with the String.Format method

String.Format如果需要将对象、变量或表达式的值插入到另一个字符串，请使用。Use String.Format if you need to insert the value of an object, variable, or expression into another string. 例如，可以将值的值插入 Decimal 字符串中，以单个字符串的形式向用户显示该值：For example, you can insert the value of a Decimal value into a string to display it to the user as a single string:

Decimal pricePerOunce = (Decimal)17.36;
String^ s = String::Format("The current price is {0} per ounce.",
                           pricePerOunce);
// Result: The current price is 17.36 per ounce.

Decimal pricePerOunce = 17.36m;
String s = String.Format("The current price is {0} per ounce.",
                         pricePerOunce);
Console.WriteLine(s);
// Result: The current price is 17.36 per ounce.

Dim pricePerOunce As Decimal = 17.36d
Dim s As String = String.Format("The current price is {0} per ounce.",
                                pricePerOunce)
' Result: The current price is 17.36 per ounce.

您可以控制该值的格式：And you can control that value's formatting:

Decimal pricePerOunce = (Decimal)17.36;
String^ s = String::Format("The current price is {0:C2} per ounce.",
                           pricePerOunce);
// Result if current culture is en-US:
//      The current price is $17.36 per ounce.

Decimal pricePerOunce = 17.36m;
String s = String.Format("The current price is {0:C2} per ounce.",
                         pricePerOunce);
Console.WriteLine(s);
// Result if current culture is en-US:
//      The current price is $17.36 per ounce.

Dim pricePerOunce As Decimal = 17.36d
Dim s As String = String.Format("The current price is {0:C2} per ounce.",
                                pricePerOunce)
' Result if current culture is en-US:
'      The current price is $17.36 per ounce.

除了格式设置，还可以控制对齐方式和间距。Besides formatting, you can also control alignment and spacing.

插入字符串Insert a string

String.Format 以格式字符串开头，后跟一个或多个将转换为字符串并在格式字符串中的指定位置插入的对象或表达式。String.Format starts with a format string, followed by one or more objects or expressions that will be converted to strings and inserted at a specified place in the format string. 例如：For example:

Decimal temp = (Decimal)20.4;
String^ s = String::Format("The temperature is {0}°C.", temp);
Console::WriteLine(s);
// Displays 'The temperature is 20.4°C.'

decimal temp = 20.4m;
string s = String.Format("The temperature is {0}°C.", temp);
Console.WriteLine(s);
// Displays 'The temperature is 20.4°C.'

Dim temp As Decimal = 20.4d
Dim s As String = String.Format("The temperature is {0}°C.", temp)
Console.WriteLine(s)
' Displays 'The temperature is 20.4°C.'

{0}格式字符串中的是格式项。The {0} in the format string is a format item. 0 对象的索引，该对象的字符串值将在该位置插入。0 is the index of the object whose string value will be inserted at that position. (索引从0开始 ) 。如果要插入的对象不是字符串，则调用它的方法将其 ToString 转换为一个字符串，然后再将其插入到结果字符串中。(Indexes start at 0.) If the object to be inserted is not a string, its ToString method is called to convert it to one before inserting it in the result string.

下面是使用两个格式项和对象列表中的两个对象的另一个示例：Here's another example that uses two format items and two objects in the object list:

String^ s = String::Format("At {0}, the temperature is {1}°C.",
                           DateTime::Now, 20.4);
// Output similar to: 'At 4/10/2015 9:29:41 AM, the temperature is 20.4°C.'

string s = String.Format("At {0}, the temperature is {1}°C.",
                         DateTime.Now, 20.4);
Console.WriteLine(s);
// Output similar to: 'At 4/10/2015 9:29:41 AM, the temperature is 20.4°C.'

Dim s As String = String.Format("At {0}, the temperature is {1}°C.",
                                Date.Now, 20.4)
' Output similar to: 'At 4/10/2015 9:29:41 AM, the temperature is 20.4°C.'

只要每个格式项的索引在对象列表中都有匹配的对象，就可以拥有任意数量的格式项以及对象列表中的任意多个对象。You can have as many format items and as many objects in the object list as you want, as long as the index of every format item has a matching object in the object list. 您也不必担心您调用的是哪个重载;编译器将为您选择合适的一个。You also don't have to worry about which overload you call; the compiler will select the appropriate one for you.

控件格式设置Control formatting

可以在格式项中的索引后跟格式字符串，以控制如何设置对象的格式。You can follow the index in a format item with a format string to control how an object is formatted. 例如， {0:d} 将 "d" 格式字符串应用于对象列表中的第一个对象。For example, {0:d} applies the "d" format string to the first object in the object list. 下面是一个包含单个对象和两个格式项的示例：Here is an example with a single object and two format items:

String^ s = String::Format("It is now {0:d} at {0:t}",
                           DateTime::Now);
// Output similar to: 'It is now 4/10/2015 at 10:04 AM'

string s = String.Format("It is now {0:d} at {0:t}", DateTime.Now);
Console.WriteLine(s);
// Output similar to: 'It is now 4/10/2015 at 10:04 AM'

Dim s As String = String.Format("It is now {0:d} at {0:t}",
                                Date.Now)
' Output similar to: 'It is now 4/10/2015 at 10:04 AM'

许多类型都支持格式字符串，其中包括标准和自定义格式字符串 (的所有数字类型) 、标准和自定义格式字符串) (的所有日期和时间均为标准和自定义格式字符串 (、所有枚举类型枚举类型以及guid。A number of types support format strings, including all numeric types (both standard and custom format strings), all dates and times (both standard and custom format strings) and time intervals (both standard and custom format strings), all enumeration types enumeration types, and GUIDs. 您还可以将对格式字符串的支持添加到您自己的类型中。You can also add support for format strings to your own types.

控件间距Control spacing

您可以通过使用诸如的语法（ {0,12} 插入12个字符的字符串）来定义插入到结果字符串中的字符串的宽度。You can define the width of the string that is inserted into the result string by using syntax such as {0,12}, which inserts a 12-character string. 在这种情况下，第一个对象的字符串表示形式在12个字符的字段中右对齐。In this case, the string representation of the first object is right-aligned in the 12-character field. (如果第一个对象的字符串表示形式的长度超过12个字符，则将忽略首选字段宽度，并将整个字符串插入到结果字符串中。 ) (If the string representation of the first object is more than 12 characters in length, though, the preferred field width is ignored, and the entire string is inserted into the result string.)

下面的示例定义了一个包含字符串 "Year" 和一些年份字符串的6字符字段，以及一个包含字符串 "人口" 和一些人口数据的15个字符的字段。The following example defines a 6-character field to hold the string "Year" and some year strings, as well as an 15-character field to hold the string "Population" and some population data. 请注意，字符在字段中右对齐。Note that the characters are right-aligned in the field.

array<int>^ years = { 2013, 2014, 2015 };
array<int>^ population = { 1025632, 1105967, 1148203 };
StringBuiler^ sb = gcnew StringBuilder();
sb->Append(String::Format("{0,6} {1,15}\n\n", "Year", "Population"));
for(int index = 0; index < years->Length; index++)
   sb->AppendFormat("{0,6} {1,15:N0}\n",
                    years[index], population[index]);
// Result:
//      Year      Population
//
//      2013       1,025,632
//      2014       1,105,967
//      2015       1,148,203

     int[] years = { 2013, 2014, 2015 };
     int[] population = { 1025632, 1105967, 1148203 };
     var sb = new System.Text.StringBuilder();
     sb.Append(String.Format("{0,6} {1,15}\n\n", "Year", "Population"));
     for (int index = 0; index < years.Length; index++)
        sb.Append(String.Format("{0,6} {1,15:N0}\n", years[index], population[index]));

     Console.WriteLine(sb);

     // Result:
     //      Year      Population
     //
     //      2013       1,025,632
     //      2014       1,105,967
     //      2015       1,148,203

Dim years() As Integer = { 2013, 2014, 2015 }
Dim population() As Integer  = { 1025632, 1105967, 1148203 }
Dim sb As New StringBuilder()
sb.Append(String.Format("{0,6} {1,15}{2}{2}",
                        "Year", "Population", vbCrLf))
For index As Integer = 0 To years.Length - 1
   sb.AppendFormat("{0,6} {1,15:N0}{2}",
                   years(index), population(index), vbCrLf)
Next
' Result:
'      Year      Population
'
'      2013       1,025,632
'      2014       1,105,967
'      2015       1,148,203

控件对齐Control alignment

默认情况下，如果指定字段宽度，则字符串在其字段内右对齐。By default, strings are right-aligned within their field if you specify a field width. 若要在字段中左对齐字符串，请在字段宽度前面加上负号，如 {0,-12} 定义12个字符左对齐字段。To left-align strings in a field, you preface the field width with a negative sign, such as {0,-12} to define a 12-character left-aligned field.

下面的示例与上一个示例类似，不同之处在于它会将标签和数据保持一致。The following example is similar to the previous one, except that it left-aligns both labels and data.

array<int>^ years = { 2013, 2014, 2015 };
array<int>^ population = { 1025632, 1105967, 1148203 };
String^ s = String::Format("{0,-10} {1,-10}\n\n", "Year", "Population");
for(int index = 0; index < years->Length; index++)
   s += String::Format("{0,-10} {1,-10:N0}\n",
                      years[index], population[index]);
// Result:
//    Year       Population
//
//    2013       1,025,632
//    2014       1,105,967
//    2015       1,148,203

int[] years = { 2013, 2014, 2015 };
int[] population = { 1025632, 1105967, 1148203 };
String s = String.Format("{0,-10} {1,-10}\n\n", "Year", "Population");
for(int index = 0; index < years.Length; index++)
   s += String.Format("{0,-10} {1,-10:N0}\n",
                      years[index], population[index]);
Console.WriteLine($"\n{s}");
// Result:
//    Year       Population
//
//    2013       1,025,632
//    2014       1,105,967
//    2015       1,148,203

Dim years() As Integer = { 2013, 2014, 2015 }
Dim population() As Integer  = { 1025632, 1105967, 1148203 }
Dim s As String = String.Format("{0,-10} {1,-10}{2}{2}",
                                "Year", "Population", vbCrLf)
For index As Integer = 0 To years.Length - 1
   s += String.Format("{0,-10} {1,-10:N0}{2}",
                      years(index), population(index), vbCrLf)
Next
' Result:
'    Year       Population
'
'    2013       1,025,632
'    2014       1,105,967
'    2015       1,148,203

String.Format 使用复合格式设置功能。String.Format makes use of the composite formatting feature. 有关更多信息，请参见复合格式设置。For more information, see Composite Formatting.

我要调用哪种方法？Which method do I call?

Format 方法 briefThe Format method in brief

该方法的每个重载都 Format 使用 复合格式设置功能 ，以复合格式字符串形式包含从零开始的索引占位符（称为 格式项）。Each overload of the Format method uses the composite formatting feature to include zero-based indexed placeholders, called format items, in a composite format string. 在运行时，每个格式项都替换为参数列表中相应参数的字符串表示形式。At run time, each format item is replaced with the string representation of the corresponding argument in a parameter list. 如果参数的值为，则 null 将格式项替换为 String.Empty 。If the value of the argument is null, the format item is replaced with String.Empty. 例如，以下对方法的调用 Format(String, Object, Object, Object) 包含一个格式字符串，其中包含三个格式项、、 {0} {1} 和 {2} ，以及包含三个项的参数列表。For example, the following call to the Format(String, Object, Object, Object) method includes a format string with three format items, {0}, {1}, and {2}, and an argument list with three items.

using namespace System;

void main()
{
   DateTime^ dat = gcnew DateTime(2012, 1, 17, 9, 30, 0); 
   String^ city = "Chicago";
   int temp = -16;
   String^ output = String::Format("At {0} in {1}, the temperature was {2} degrees.",
                                   dat, city, temp);
   Console::WriteLine(output);
}
// The example displays the following output: 
//    At 1/17/2012 9:30:00 AM in Chicago, the temperature was -16 degrees.   

DateTime dat = new DateTime(2012, 1, 17, 9, 30, 0); 
string city = "Chicago";
int temp = -16;
string output = String.Format("At {0} in {1}, the temperature was {2} degrees.",
                              dat, city, temp);
Console.WriteLine(output);
// The example displays output like the following:
//    At 1/17/2012 9:30:00 AM in Chicago, the temperature was -16 degrees.   

Dim dat As Date = #1/17/2012 9:30AM# 
Dim city As String = "Chicago"
Dim temp As Integer = -16
Dim output As String = String.Format("At {0} in {1}, the temperature was {2} degrees.",
                                     dat, city, temp)
Console.WriteLine(output)
' The example displays the following output:
'    At 1/17/2012 9:30:00 AM in Chicago, the temperature was -16 degrees.   

格式项The format item

格式项具有以下语法：A format item has this syntax:

{index[,alignment][:formatString]}

方括号表示可选元素。Brackets denote optional elements. 需要左大括号和右大括号。The opening and closing braces are required. (在格式字符串中包含文本左大括号或右大括号，请参阅复合格式设置一文中的转义大括号部分。 ) (To include a literal opening or closing brace in the format string, see the Escaping Braces section in the Composite Formatting article.)

例如，设置货币值格式的格式项可能如下所示：For example, a format item to format a currency value might appear like this:

String::Format("{0,-10:C}", (Decimal) 126347.89);         

var value = String.Format("{0,-10:C}", 126347.89m);         
Console.WriteLine(value);

String.Format("{0,-10:C}", 126347.89d)        

格式项包含以下元素：A format item has the following elements:

indexindex
自变量的从零开始的索引，其字符串表示形式将包含在字符串中的此位置。The zero-based index of the argument whose string representation is to be included at this position in the string. 如果此参数为 null ，则字符串中此位置将包含空字符串。If this argument is null, an empty string will be included at this position in the string.

关联alignment
可选。Optional. 一个有符号整数，它指示要插入自变量的字段的总长度，并指定该参数是右对齐的， (是正整数) 还是) 负整数 (左对齐。A signed integer that indicates the total length of the field into which the argument is inserted and whether it is right-aligned (a positive integer) or left-aligned (a negative integer). 如果省略 对齐方式，则会在不带前导空格或尾随空格的字段中插入相应参数的字符串表示形式。If you omit alignment, the string representation of the corresponding argument is inserted in a field with no leading or trailing spaces.

如果 对齐 值小于要插入的参数的长度，则将忽略 对齐 ，并使用参数的字符串表示形式的长度作为字段宽度。If the value of alignment is less than the length of the argument to be inserted, alignment is ignored and the length of the string representation of the argument is used as the field width.

说明符formatString
可选。Optional. 一个字符串，指定相应参数的结果字符串的格式。A string that specifies the format of the corresponding argument's result string. 如果省略 格式说明符，则将调用相应的参数的无参数 ToString 方法，以生成其字符串表示形式。If you omit formatString, the corresponding argument's parameterless ToString method is called to produce its string representation. 如果指定格式 字符串，则该格式项引用的参数必须实现 IFormattable 接口。If you specify formatString, the argument referenced by the format item must implement the IFormattable interface. 支持格式字符串的类型包括：Types that support format strings include:

• 所有整型和浮点类型。All integral and floating-point types. (参见 标准数字格式字符串 和 自定义数字格式字符串。 ) (See Standard Numeric Format Strings and Custom Numeric Format Strings.)

• DateTime 和 DateTimeOffset。DateTime and DateTimeOffset. (参见 标准日期和时间格式字符串 和 自定义日期和时间格式字符串。 ) (See Standard Date and Time Format Strings and Custom Date and Time Format Strings.)

• 所有枚举类型。All enumeration types. (参见 枚举格式字符串。 ) (See Enumeration Format Strings.)

• TimeSpan 值。TimeSpan values. (参见 标准 Timespan 格式字符串 和 自定义时间跨度格式字符串。 ) (See Standard TimeSpan Format Strings and Custom TimeSpan Format Strings.)

• GUID。GUIDs. (参见 Guid.ToString(String) 方法。 ) (See the Guid.ToString(String) method.)

但请注意，任何自定义类型都可以实现 IFormattable 或扩展现有类型的 IFormattable 实现。However, note that any custom type can implement IFormattable or extend an existing type's IFormattable implementation.

下面的示例使用 alignment 和 formatString 参数来生成格式化的输出。The following example uses the alignment and formatString arguments to produce formatted output.

using namespace System;

void main()
{
   // Create array of 5-tuples with population data for three U.S. cities, 1940-1950.
   array<Tuple<String^, DateTime, int, DateTime, int>^>^ cities = gcnew array<Tuple<String^, DateTime, int, DateTime, int>^> 
         { gcnew Tuple<String^, DateTime, int, DateTime, int>("Los Angeles", DateTime(1940, 1, 1), 1504277, 
                        DateTime(1950, 1, 1), 1970358),
         gcnew Tuple<String^, DateTime, int, DateTime, int>("New York", DateTime(1940, 1, 1), 7454995, 
                        DateTime(1950, 1, 1), 7891957),  
         gcnew Tuple<String^, DateTime, int, DateTime, int>("Chicago", DateTime(1940, 1, 1), 3396808, 
                        DateTime(1950, 1, 1), 3620962),  
         gcnew Tuple<String^, DateTime, int, DateTime, int>("Detroit", DateTime(1940, 1, 1), 1623452, 
                        DateTime(1950, 1, 1), 1849568) };

   // Display header
   String^ header = String::Format("{0,-12}{1,8}{2,12}{1,8}{2,12}{3,14}\n",
                                   "City", "Year", "Population", "Change (%)");
   Console::WriteLine(header);
   String^ output;      
   for each (Tuple<String^, DateTime, int, DateTime, int>^ city in cities) {
      output = String::Format("{0,-12}{1,8:yyyy}{2,12:N0}{3,8:yyyy}{4,12:N0}{5,14:P1}",
                              city->Item1, city->Item2, city->Item3, city->Item4, city->Item5,
                              (city->Item5 - city->Item3)/ (double)city->Item3);
      Console::WriteLine(output);
   }
}
// The example displays the following output:
//    City            Year  Population    Year  Population    Change (%)
//    
//    Los Angeles     1940   1,504,277    1950   1,970,358        31.0 %
//    New York        1940   7,454,995    1950   7,891,957         5.9 %
//    Chicago         1940   3,396,808    1950   3,620,962         6.6 %
//    Detroit         1940   1,623,452    1950   1,849,568        13.9 %

// Create array of 5-tuples with population data for three U.S. cities, 1940-1950.
Tuple<string, DateTime, int, DateTime, int>[] cities = 
    { Tuple.Create("Los Angeles", new DateTime(1940, 1, 1), 1504277, 
                   new DateTime(1950, 1, 1), 1970358),
      Tuple.Create("New York", new DateTime(1940, 1, 1), 7454995, 
                   new DateTime(1950, 1, 1), 7891957),  
      Tuple.Create("Chicago", new DateTime(1940, 1, 1), 3396808, 
                   new DateTime(1950, 1, 1), 3620962),  
      Tuple.Create("Detroit", new DateTime(1940, 1, 1), 1623452, 
                   new DateTime(1950, 1, 1), 1849568) };

// Display header
var header = String.Format("{0,-12}{1,8}{2,12}{1,8}{2,12}{3,14}\n",
                              "City", "Year", "Population", "Change (%)");
Console.WriteLine(header);
foreach (var city in cities) {
   var output = String.Format("{0,-12}{1,8:yyyy}{2,12:N0}{3,8:yyyy}{4,12:N0}{5,14:P1}",
                          city.Item1, city.Item2, city.Item3, city.Item4, city.Item5,
                          (city.Item5 - city.Item3)/ (double)city.Item3);
   Console.WriteLine(output);
}
// The example displays the following output:
//    City            Year  Population    Year  Population    Change (%)
//  
//    Los Angeles     1940   1,504,277    1950   1,970,358        31.0 %
//    New York        1940   7,454,995    1950   7,891,957         5.9 %
//    Chicago         1940   3,396,808    1950   3,620,962         6.6 %
//    Detroit         1940   1,623,452    1950   1,849,568        13.9 %

Module Example
   Public Sub Main()
      ' Create array of 5-tuples with population data for three U.S. cities, 1940-1950.
      Dim cities()  = _
          { Tuple.Create("Los Angeles", #1/1/1940#, 1504277, #1/1/1950#, 1970358),
            Tuple.Create("New York", #1/1/1940#, 7454995, #1/1/1950#, 7891957),  
            Tuple.Create("Chicago", #1/1/1940#, 3396808, #1/1/1950#, 3620962),  
            Tuple.Create("Detroit", #1/1/1940#, 1623452, #1/1/1950#, 1849568) }

      ' Display header
      Dim header As String = String.Format("{0,-12}{1,8}{2,12}{1,8}{2,12}{3,14}",
                                           "City", "Year", "Population", "Change (%)")
      Console.WriteLine(header)
      Console.WriteLine()
      For Each city In cities
         Dim output = String.Format("{0,-12}{1,8:yyyy}{2,12:N0}{3,8:yyyy}{4,12:N0}{5,14:P1}",
                                city.Item1, city.Item2, city.Item3, city.Item4, city.Item5,
                                (city.Item5 - city.Item3)/city.Item3)
         Console.WriteLine(output)
      Next
   End Sub
End Module
' The example displays the following output:
'    City            Year  Population    Year  Population    Change (%)
'    
'    Los Angeles     1940   1,504,277    1950   1,970,358        31.0 %
'    New York        1940   7,454,995    1950   7,891,957         5.9 %
'    Chicago         1940   3,396,808    1950   3,620,962         6.6 %
'    Detroit         1940   1,623,452    1950   1,849,568        13.9 %

如何设置参数的格式How arguments are formatted

格式项从字符串的开头按顺序处理。Format items are processed sequentially from the beginning of the string. 每个格式项都具有与方法的参数列表中的对象相对应的索引。Each format item has an index that corresponds to an object in the method's argument list. Format方法检索参数并按如下方式派生其字符串表示形式：The Format method retrieves the argument and derives its string representation as follows:

• 如果参数为 null ，则该方法将插入 String.Empty 到结果字符串中。If the argument is null, the method inserts String.Empty into the result string. 不必担心如何处理 NullReferenceException null 参数。You don't have to be concerned with handling a NullReferenceException for null arguments.

• 如果调用 Format(IFormatProvider, String, Object[]) 重载并且 provider 对象的 IFormatProvider.GetFormat 实现返回非 null ICustomFormatter 实现，则会将参数传递给其 ICustomFormatter.Format(String, Object, IFormatProvider) 方法。If you call the Format(IFormatProvider, String, Object[]) overload and the provider object's IFormatProvider.GetFormat implementation returns a non-null ICustomFormatter implementation, the argument is passed to its ICustomFormatter.Format(String, Object, IFormatProvider) method. 如果格式项包含格式 字符串 参数，则它将作为第一个参数传递给方法。If the format item includes a formatString argument, it is passed as the first argument to the method. 如果 ICustomFormatter 实现可用并且产生一个非空字符串，则返回该字符串作为参数的字符串表示形式; 否则，将执行下一步。If the ICustomFormatter implementation is available and produces a non-null string, that string is returned as the string representation of the argument; otherwise, the next step executes.

• 如果参数实现 IFormattable 接口， IFormattable.ToString 则调用其实现。If the argument implements the IFormattable interface, its IFormattable.ToString implementation is called.

• 调用了自变量的无参数 ToString 方法，该方法可重写或继承基类实现。The argument's parameterless ToString method, which either overrides or inherits from a base class implementation, is called.

有关截获对方法的调用， ICustomFormatter.Format 并允许你查看 Format 方法为复合格式字符串中的每个格式项传递到格式设置方法的信息，请参阅 示例：截获提供程序和罗马数字格式化程序。For an example that intercepts calls to the ICustomFormatter.Format method and allows you to see what information the Format method passes to a formatting method for each format item in a composite format string, see Example: An intercept provider and Roman numeral formatter.

有关详细信息，请参阅复合格式设置一文中的 "处理顺序" 部分。For more information, see the Processing Order section in the Composite Formatting article.

设置具有相同索引的项的格式Format items that have the same index

Format FormatException 如果索引项的索引大于或等于参数列表中的参数数目，则该方法将引发异常。The Format method throws a FormatException exception if the index of an index item is greater than or equal to the number of arguments in the argument list. 但是， format 只要多个格式项具有相同的索引，就可以包含比参数更多的格式项。However, format can include more format items than there are arguments, as long as multiple format items have the same index. 在以下示例中，对方法的调用中 Format(String, Object) ，参数列表具有单个参数，但格式字符串包含两个格式项：一个显示数字的十进制值，另一个显示其十六进制值。In the call to the Format(String, Object) method in following example, the argument list has a single argument, but the format string includes two format items: one displays the decimal value of a number, and the other displays its hexadecimal value.

short[] values= { Int16.MinValue, -27, 0, 1042, Int16.MaxValue };
Console.WriteLine("{0,10}  {1,10}\n", "Decimal", "Hex");
foreach (short value in values)
{
   string formatString = String.Format("{0,10:G}: {0,10:X}", value);
   Console.WriteLine(formatString);
}   
// The example displays the following output:
//       Decimal         Hex
//    
//        -32768:       8000
//           -27:       FFE5
//             0:          0
//          1042:        412
//         32767:       7FFF

Module Example
   Public Sub Main()
      Dim values() As Short = { Int16.MinValue, -27, 0, 1042, Int16.MaxValue }
      Console.WriteLine("{0,10}  {1,10}", "Decimal", "Hex")
      Console.WriteLine()
      For Each value As Short In values
         Dim formatString As String = String.Format("{0,10:G}: {0,10:X}", value)
         Console.WriteLine(formatString)
      Next        
   End Sub
End Module
' The example displays the following output:
'       Decimal         Hex
'    
'        -32768:       8000
'           -27:       FFE5
'             0:          0
'          1042:        412
'         32767:       7FFF

格式和区域性Format and culture

通常，使用当前区域性的约定（由属性返回），将参数列表中的对象转换为其字符串表示形式 CultureInfo.CurrentCulture 。Generally, objects in the argument list are converted to their string representations by using the conventions of the current culture, which is returned by the CultureInfo.CurrentCulture property. 可以通过调用包含参数的的重载之一来控制此行为 Format provider 。You can control this behavior by calling one of the overloads of Format that includes a provider parameter. provider参数是一个 IFormatProvider 实现，提供用于使格式设置过程适中的自定义和区域性特定的格式设置信息。The provider parameter is an IFormatProvider implementation that supplies custom and culture-specific formatting information that is used to moderate the formatting process.

此 IFormatProvider 接口具有一个成员， GetFormat 该成员负责返回提供格式设置信息的对象。The IFormatProvider interface has a single member, GetFormat, which is responsible for returning the object that provides formatting information. .NET 具有三种 IFormatProvider 实现，它们提供区域性特定的格式设置：.NET has three IFormatProvider implementations that provide culture-specific formatting:

• CultureInfo.CultureInfo. 其 GetFormat 方法返回一个特定于区域性的 NumberFormatInfo 对象，用于设置数值的格式，以及 DateTimeFormatInfo 用于设置日期和时间值格式的区域性特定的对象。Its GetFormat method returns a culture-specific NumberFormatInfo object for formatting numeric values and a culture-specific DateTimeFormatInfo object for formatting date and time values.

• DateTimeFormatInfo，它用于日期和时间值的区域性特定格式设置。DateTimeFormatInfo, which is used for culture-specific formatting of date and time values. 其 GetFormat 方法返回自身。Its GetFormat method returns itself.

• NumberFormatInfo，它用于指定数值的区域性特定格式。NumberFormatInfo, which is used for culture-specific formatting of numeric values. 其 GetFormat 属性返回自身。Its GetFormat property returns itself.

自定义格式设置操作Custom formatting operations

您还可以调用 Format 具有类型的参数的方法的任何重载 provider IFormatProvider 来执行自定义格式设置操作。You can also call the any of the overloads of the Format method that have a provider parameter of type IFormatProvider to perform custom formatting operations. 例如，可以将整数的格式设置为标识号或电话号码。For example, you could format an integer as an identification number or as a telephone number. 若要执行自定义格式设置，你 provider 的参数必须实现 IFormatProvider 和 ICustomFormatter 接口。To perform custom formatting, your provider argument must implement both the IFormatProvider and ICustomFormatter interfaces. 当向 Format 方法传递 ICustomFormatter 实现作为 provider 参数时， Format 方法将调用其 IFormatProvider.GetFormat 实现并请求类型的对象 ICustomFormatter 。When the Format method is passed an ICustomFormatter implementation as the provider argument, the Format method calls its IFormatProvider.GetFormat implementation and requests an object of type ICustomFormatter. 然后，它调用返回的 ICustomFormatter 对象的 Format 方法，以设置传递给它的复合字符串中的每个格式项的格式。It then calls the returned ICustomFormatter object's Format method to format each format item in the composite string passed to it.

有关提供自定义格式设置解决方案的详细信息，请参阅 如何：定义和使用自定义数值格式提供程序 和 ICustomFormatter 。For more information about providing custom formatting solutions, see How to: Define and Use Custom Numeric Format Providers and ICustomFormatter. 有关将整数转换为格式化自定义数字的示例，请参阅 示例：自定义格式设置操作。For an example that converts integers to formatted custom numbers, see Example: A custom formatting operation. 有关将无符号字节转换为罗马数字的示例，请参阅 示例：截获提供程序和罗马数字格式化程序。For an example that converts unsigned bytes to Roman numerals, see Example: An intercept provider and Roman numeral formatter.

示例：自定义格式设置操作Example: A custom formatting operation

此示例定义格式提供程序，该提供程序将整数值的格式设置为 x-xxxxx-xx 形式的客户帐户号。This example defines a format provider that formats an integer value as a customer account number in the form x-xxxxx-xx.

using namespace System;

ref class CustomerFormatter : IFormatProvider, ICustomFormatter
{
public:
   virtual Object^ GetFormat(Type^ formatType) 
   {
      if (formatType == ICustomFormatter::typeid)        
         return this; 
      else 
         return nullptr; 
   }
   
   virtual String^ Format(String^ format, 
                   Object^ arg, 
                   IFormatProvider^ formatProvider) 
   {                       
      if (! this->Equals(formatProvider))
      {
         return nullptr;
      }
      else
      {
         if (String::IsNullOrEmpty(format)) 
            format = "G";
         
         String^ customerString = arg->ToString();
         if (customerString->Length < 8)
            customerString = customerString->PadLeft(8, '0');
         
         format = format->ToUpper();
         if (format == L"G") 
               return customerString->Substring(0, 1) + "-" +
                                     customerString->Substring(1, 5) + "-" +
                                     customerString->Substring(6);
         else if (format == L"S")                          
               return customerString->Substring(0, 1) + "/" +
                                     customerString->Substring(1, 5) + "/" +
                                     customerString->Substring(6);
         else if (format == L"P")
               return customerString->Substring(0, 1) + "." +
                                     customerString->Substring(1, 5) + "." +
                                     customerString->Substring(6);
         else
               throw gcnew FormatException( 
                         String::Format("The '{0}' format specifier is not supported.", format));
         }
    }   
};

void main()
{
   int acctNumber = 79203159;
   Console::WriteLine(String::Format(gcnew CustomerFormatter, "{0}", acctNumber));
   Console::WriteLine(String::Format(gcnew CustomerFormatter, "{0:G}", acctNumber));
   Console::WriteLine(String::Format(gcnew CustomerFormatter, "{0:S}", acctNumber));
   Console::WriteLine(String::Format(gcnew CustomerFormatter, "{0:P}", acctNumber));
   try {
      Console::WriteLine(String::Format(gcnew CustomerFormatter, "{0:X}", acctNumber));
   }
   catch (FormatException^ e) {
      Console::WriteLine(e->Message);
   }
}
// The example displays the following output:
//       7-92031-59
//       7-92031-59
//       7/92031/59
//       7.92031.59
//       The 'X' format specifier is not supported.

using System;

public class TestFormatter
{
   public static void Main()
   {
      int acctNumber = 79203159;
      Console.WriteLine(String.Format(new CustomerFormatter(), "{0}", acctNumber));
      Console.WriteLine(String.Format(new CustomerFormatter(), "{0:G}", acctNumber));
      Console.WriteLine(String.Format(new CustomerFormatter(), "{0:S}", acctNumber));
      Console.WriteLine(String.Format(new CustomerFormatter(), "{0:P}", acctNumber));
      try {
         Console.WriteLine(String.Format(new CustomerFormatter(), "{0:X}", acctNumber));
      }
      catch (FormatException e) {
         Console.WriteLine(e.Message);
      }
   }
}

public class CustomerFormatter : IFormatProvider, ICustomFormatter
{
   public object GetFormat(Type formatType) 
   {
      if (formatType == typeof(ICustomFormatter))        
         return this; 
      else
         return null;
   }
   
   public string Format(string format, 
                         object arg, 
                         IFormatProvider formatProvider) 
   {                       
      if (! this.Equals(formatProvider))
      {
         return null;
      }
      else
      {
         if (String.IsNullOrEmpty(format)) 
            format = "G";
         
         string customerString = arg.ToString();
         if (customerString.Length < 8)
            customerString = customerString.PadLeft(8, '0');
         
         format = format.ToUpper();
         switch (format)
         {
            case "G":
               return customerString.Substring(0, 1) + "-" +
                                     customerString.Substring(1, 5) + "-" +
                                     customerString.Substring(6);
            case "S":                          
               return customerString.Substring(0, 1) + "/" +
                                     customerString.Substring(1, 5) + "/" +
                                     customerString.Substring(6);
            case "P":                          
               return customerString.Substring(0, 1) + "." +
                                     customerString.Substring(1, 5) + "." +
                                     customerString.Substring(6);
            default:
               throw new FormatException( 
                         String.Format("The '{0}' format specifier is not supported.", format));
         }
      }   
   }
}
// The example displays the following output:
//       7-92031-59
//       7-92031-59
//       7/92031/59
//       7.92031.59
//       The 'X' format specifier is not supported.

Module TestFormatter
   Public Sub Main()
      Dim acctNumber As Integer = 79203159
      Console.WriteLine(String.Format(New CustomerFormatter, "{0}", acctNumber))
      Console.WriteLine(String.Format(New CustomerFormatter, "{0:G}", acctNumber))
      Console.WriteLine(String.Format(New CustomerFormatter, "{0:S}", acctNumber))
      Console.WriteLine(String.Format(New CustomerFormatter, "{0:P}", acctNumber))
      Try
         Console.WriteLine(String.Format(New CustomerFormatter, "{0:X}", acctNumber))
      Catch e As FormatException
         Console.WriteLine(e.Message)
      End Try   
   End Sub
End Module

Public Class CustomerFormatter : Implements IFormatProvider, ICustomFormatter
   Public Function GetFormat(type As Type) As Object  _
                   Implements IFormatProvider.GetFormat
      If type Is GetType(ICustomFormatter) Then
         Return Me
      Else
         Return Nothing
      End If
   End Function
   
   Public Function Format(fmt As String, _
                           arg As Object, _
                           formatProvider As IFormatProvider) As String _
                    Implements ICustomFormatter.Format
      If Not Me.Equals(formatProvider) Then
         Return Nothing
      Else
         If String.IsNullOrEmpty(fmt) Then fmt = "G"
         
         Dim customerString As String = arg.ToString()
         if customerString.Length < 8 Then _
            customerString = customerString.PadLeft(8, "0"c)
         
         Select Case fmt
            Case "G"
               Return customerString.Substring(0, 1) & "-" & _
                                     customerString.Substring(1, 5) & "-" & _
                                     customerString.Substring(6)
            Case "S"                         
               Return customerString.Substring(0, 1) & "/" & _
                                     customerString.Substring(1, 5) & "/" & _
                                     customerString.Substring(6)
            Case "P"
               Return customerString.Substring(0, 1) & "." & _
                                     customerString.Substring(1, 5) & "." & _
                                     customerString.Substring(6)
            Case Else
               Throw New FormatException( _
                         String.Format("The '{0}' format specifier is not supported.", fmt))
         End Select                                                     
      End If   
   End Function
End Class
' The example displays the following output:
'       7-92031-59
'       7-92031-59
'       7/92031/59
'       7.92031.59
'       The 'X' format specifier is not supported.

示例：截距提供程序和罗马数字格式化程序Example: An intercept provider and Roman numeral formatter

此示例定义了一个自定义格式提供程序，该提供程序实现 ICustomFormatter 和 IFormatProvider 接口以执行两项操作：This example defines a custom format provider that implements the ICustomFormatter and IFormatProvider interfaces to do two things:

• 它将显示传递到其实现的参数 ICustomFormatter.Format 。It displays the parameters passed to its ICustomFormatter.Format implementation. 这使我们能够查看方法将哪些参数 Format(IFormatProvider, String, Object[]) 传递到其尝试设置格式的每个对象的自定义格式设置实现。This enables us to see what parameters the Format(IFormatProvider, String, Object[]) method is passing to the custom formatting implementation for each object that it tries to format. 调试应用程序时，这会很有用。This can be useful when you're debugging your application.

• 如果要设置格式的对象是要使用 "R" 标准格式字符串设置格式的无符号字节值，则自定义格式化程序将数值的格式设置为罗马数字。If the object to be formatted is an unsigned byte value that is to be formatted by using the "R" standard format string, the custom formatter formats the numeric value as a Roman numeral.

using namespace System;
using namespace System::Globalization;

ref class InterceptProvider : IFormatProvider, ICustomFormatter
{
public:
   virtual Object^ GetFormat(Type^ formatType)
   {
      if (formatType == ICustomFormatter::typeid)   
         return this;
      else
         return nullptr;
   }
   
   virtual String^ Format(String^ format, Object^ obj, IFormatProvider^ provider) 
   {
      // Display information about method call.
      String^ formatString = format != nullptr ? format : "<null>";
      Console::WriteLine("Provider: {0}, Object: {1}, Format String: {2}",
                        provider, obj != nullptr ? obj : "<null>", formatString);
                        
      if (obj == nullptr) return String::Empty;
            
      // If this is a byte and the "R" format string, format it with Roman numerals.
      if (obj->GetType() == Byte::typeid && formatString->ToUpper()->Equals("R")) {
         Byte value = (Byte) obj;
         int remainder;
         int result;
         String^ returnString = String::Empty;

         // Get the hundreds digit(s)
         result = Math::DivRem(value, 100, remainder);
         if (result > 0)  
            returnString = gcnew String('C', result);
         value = (Byte) remainder;
         // Get the 50s digit
         result = Math::DivRem(value, 50, remainder);
         if (result == 1)
            returnString += "L";
         value = (Byte) remainder;
         // Get the tens digit.
         result = Math::DivRem(value, 10, remainder);
         if (result > 0)
            returnString += gcnew String('X', result);
         value = (Byte) remainder; 
         // Get the fives digit.
         result = Math::DivRem(value, 5, remainder);
         if (result > 0)
            returnString += "V";
         value = (Byte) remainder;
         // Add the ones digit.
         if (remainder > 0) 
            returnString += gcnew String('I', remainder);
         
         // Check whether we have too many X characters.
         int pos = returnString->IndexOf("XXXX");
         if (pos >= 0) {
            int xPos = returnString->IndexOf("L"); 
            if ((xPos >= 0) & (xPos == pos - 1))
               returnString = returnString->Replace("LXXXX", "XC");
            else
               returnString = returnString->Replace("XXXX", "XL");   
         }
         // Check whether we have too many I characters
         pos = returnString->IndexOf("IIII");
         if (pos >= 0)
            if (returnString->IndexOf("V") >= 0)
               returnString = returnString->Replace("VIIII", "IX");
            else
               returnString = returnString->Replace("IIII", "IV");    

         return returnString; 
      }   

      // Use default for all other formatting.
      if (obj->GetType() == IFormattable::typeid)
         return ((IFormattable^) obj)->ToString(format, CultureInfo::CurrentCulture);
      else
         return obj->ToString();
   }
};

void main()
{
   int n = 10;
   double value = 16.935;
   DateTime day = DateTime::Now;
   InterceptProvider^ provider = gcnew InterceptProvider();
   Console::WriteLine(String::Format(provider, "{0:N0}: {1:C2} on {2:d}\n", n, value, day));
   Console::WriteLine(String::Format(provider, "{0}: {1:F}\n", "Today: ", 
                                    (DayOfWeek) DateTime::Now.DayOfWeek));
   Console::WriteLine(String::Format(provider, "{0:X}, {1}, {2}\n", 
                                    (Byte) 2, (Byte) 12, (Byte) 199));
   Console::WriteLine(String::Format(provider, "{0:R}, {1:R}, {2:R}\n", 
                                    (Byte) 2, (Byte) 12, (Byte) 199));
}
// The example displays the following output:
//    Provider: InterceptProvider, Object: 10, Format String: N0
//    Provider: InterceptProvider, Object: 16.935, Format String: C2
//    Provider: InterceptProvider, Object: 1/31/2013 6:10:28 PM, Format String: d
//    10: $16.94 on 1/31/2013
//    
//    Provider: InterceptProvider, Object: Today: , Format String: <null>
//    Provider: InterceptProvider, Object: Thursday, Format String: F
//    Today: : Thursday
//    
//    Provider: InterceptProvider, Object: 2, Format String: X
//    Provider: InterceptProvider, Object: 12, Format String: <null>
//    Provider: InterceptProvider, Object: 199, Format String: <null>
//    2, 12, 199
//    
//    Provider: InterceptProvider, Object: 2, Format String: R
//    Provider: InterceptProvider, Object: 12, Format String: R
//    Provider: InterceptProvider, Object: 199, Format String: R
//    II, XII, CXCIX

using System;
using System.Globalization;

public class InterceptProvider : IFormatProvider, ICustomFormatter
{
   public object GetFormat(Type formatType)
   {
      if (formatType == typeof(ICustomFormatter))
         return this;
      else
         return null;
   }
   
   public string Format(String format, Object obj, IFormatProvider provider) 
   {
      // Display information about method call.
      string formatString = format ?? "<null>";
      Console.WriteLine("Provider: {0}, Object: {1}, Format String: {2}",
                        provider.GetType().Name, obj ?? "<null>", formatString);
                        
      if (obj == null) return String.Empty;
            
      // If this is a byte and the "R" format string, format it with Roman numerals.
      if (obj is Byte && formatString.ToUpper().Equals("R")) {
         Byte value = (Byte) obj;
         int remainder;
         int result;
         String returnString = String.Empty;

         // Get the hundreds digit(s)
         result = Math.DivRem(value, 100, out remainder);
         if (result > 0)  
            returnString = new String('C', result);
         value = (Byte) remainder;
         // Get the 50s digit
         result = Math.DivRem(value, 50, out remainder);
         if (result == 1)
            returnString += "L";
         value = (Byte) remainder;
         // Get the tens digit.
         result = Math.DivRem(value, 10, out remainder);
         if (result > 0)
            returnString += new String('X', result);
         value = (Byte) remainder; 
         // Get the fives digit.
         result = Math.DivRem(value, 5, out remainder);
         if (result > 0)
            returnString += "V";
         value = (Byte) remainder;
         // Add the ones digit.
         if (remainder > 0) 
            returnString += new String('I', remainder);
         
         // Check whether we have too many X characters.
         int pos = returnString.IndexOf("XXXX");
         if (pos >= 0) {
            int xPos = returnString.IndexOf("L"); 
            if (xPos >= 0 & xPos == pos - 1)
               returnString = returnString.Replace("LXXXX", "XC");
            else
               returnString = returnString.Replace("XXXX", "XL");   
         }
         // Check whether we have too many I characters
         pos = returnString.IndexOf("IIII");
         if (pos >= 0)
            if (returnString.IndexOf("V") >= 0)
               returnString = returnString.Replace("VIIII", "IX");
            else
               returnString = returnString.Replace("IIII", "IV");    

         return returnString; 
      }   

      // Use default for all other formatting.
      if (obj is IFormattable)
         return ((IFormattable) obj).ToString(format, CultureInfo.CurrentCulture);
      else
         return obj.ToString();
   }
}

public class Example
{
   public static void Main()
   {
      int n = 10;
      double value = 16.935;
      DateTime day = DateTime.Now;
      InterceptProvider provider = new InterceptProvider();
      Console.WriteLine(String.Format(provider, "{0:N0}: {1:C2} on {2:d}\n", n, value, day));
      Console.WriteLine(String.Format(provider, "{0}: {1:F}\n", "Today: ", 
                                      (DayOfWeek) DateTime.Now.DayOfWeek));
      Console.WriteLine(String.Format(provider, "{0:X}, {1}, {2}\n", 
                                      (Byte) 2, (Byte) 12, (Byte) 199));
      Console.WriteLine(String.Format(provider, "{0:R}, {1:R}, {2:R}\n", 
                                      (Byte) 2, (Byte) 12, (Byte) 199));
   }
}
// The example displays the following output:
//    Provider: InterceptProvider, Object: 10, Format String: N0
//    Provider: InterceptProvider, Object: 16.935, Format String: C2
//    Provider: InterceptProvider, Object: 1/31/2013 6:10:28 PM, Format String: d
//    10: $16.94 on 1/31/2013
//    
//    Provider: InterceptProvider, Object: Today: , Format String: <null>
//    Provider: InterceptProvider, Object: Thursday, Format String: F
//    Today: : Thursday
//    
//    Provider: InterceptProvider, Object: 2, Format String: X
//    Provider: InterceptProvider, Object: 12, Format String: <null>
//    Provider: InterceptProvider, Object: 199, Format String: <null>
//    2, 12, 199
//    
//    Provider: InterceptProvider, Object: 2, Format String: R
//    Provider: InterceptProvider, Object: 12, Format String: R
//    Provider: InterceptProvider, Object: 199, Format String: R
//    II, XII, CXCIX

Imports System.Globalization

Public Class InterceptProvider : Implements IFormatProvider, ICustomFormatter
   Public Function GetFormat(formatType As Type) As Object _
         Implements IFormatProvider.GetFormat
      If formatType Is GetType(ICustomFormatter) Then
         Return Me
      Else
         Return Nothing
      End If
   End Function
   
   Public Function Format(fmt As String, obj As Object, provider As IFormatProvider) As String _
         Implements ICustomFormatter.Format

      Dim formatString As String = If(fmt IsNot Nothing, fmt, "<null>")
      Console.WriteLine("Provider: {0}, Object: {1}, Format String: {2}",
                        provider, If(obj IsNot Nothing, obj, "<null>"), formatString)

      If obj Is Nothing Then Return String.Empty
            
      ' If this is a byte and the "R" format string, format it with Roman numerals.
      If TypeOf(obj) Is Byte AndAlso formatString.ToUpper.Equals("R") Then
         Dim value As Byte = CByte(obj)
         Dim remainder As Integer
         Dim result As Integer
         Dim returnString As String = String.Empty

         ' Get the hundreds digit(s)
         result = Math.DivRem(value, 100, remainder)
         If result > 0 Then returnString = New String("C"c, result)
         value = CByte(remainder)
         ' Get the 50s digit
         result = Math.DivRem(value, 50, remainder)
         If result = 1 Then returnString += "L"
         value = CByte(remainder)
         ' Get the tens digit.
         result = Math.DivRem(value, 10, remainder)
         If result > 0 Then returnString += New String("X"c, result)
         value = CByte(remainder) 
         ' Get the fives digit.
         result = Math.DivRem(value, 5, remainder)
         If result > 0 Then returnString += "V"
         value = CByte(remainder)
         ' Add the ones digit.
         If remainder > 0 Then returnString += New String("I"c, remainder)
         
         ' Check whether we have too many X characters.
         Dim pos As Integer = returnString.IndexOf("XXXX")
         If pos >= 0 Then
            Dim xPos As Integer = returnString.IndexOf("L") 
            If xPos >= 0 And xPos = pos - 1 Then
               returnString = returnString.Replace("LXXXX", "XC")
            Else
               returnString = returnString.Replace("XXXX", "XL")   
            End If         
         End If
         ' Check whether we have too many I characters
         pos = returnString.IndexOf("IIII")
         If pos >= 0 Then
            If returnString.IndexOf("V") >= 0 Then
               returnString = returnString.Replace("VIIII", "IX")
            Else
               returnString = returnString.Replace("IIII", "IV")    
            End If
         End If
         Return returnString 
      End If   

      ' Use default for all other formatting.
      If obj Is GetType(IFormattable)
         Return CType(obj, IFormattable).ToString(fmt, CultureInfo.CurrentCulture)
      Else
         Return obj.ToString()
      End If
   End Function
End Class

Module Example
   Public Sub Main()
      Dim n As Integer = 10
      Dim value As Double = 16.935
      Dim day As DateTime = Date.Now
      Dim provider As New InterceptProvider()
      Console.WriteLine(String.Format(provider, "{0:N0}: {1:C2} on {2:d}", n, value, day))
      Console.WriteLine()
      Console.WriteLine(String.Format(provider, "{0}: {1:F}", "Today", 
                                      CType(Date.Now.DayOfWeek, DayOfWeek)))
      Console.WriteLine()
      Console.WriteLine(String.Format(provider, "{0:X}, {1}, {2}\n", 
                                      CByte(2), CByte(12), CByte(199)))
      Console.WriteLine()
      Console.WriteLine(String.Format(provider, "{0:R}, {1:R}, {2:R}", 
                                      CByte(2), CByte(12), CByte(199)))
   End Sub
End Module
' The example displays the following output:
'    Provider: InterceptProvider, Object: 10, Format String: N0
'    Provider: InterceptProvider, Object: 16.935, Format String: C2
'    Provider: InterceptProvider, Object: 1/31/2013 6:10:28 PM, Format String: d
'    10: $16.94 on 1/31/2013
'    
'    Provider: InterceptProvider, Object: Today: , Format String: <null>
'    Provider: InterceptProvider, Object: Thursday, Format String: F
'    Today: : Thursday
'    
'    Provider: InterceptProvider, Object: 2, Format String: X
'    Provider: InterceptProvider, Object: 12, Format String: <null>
'    Provider: InterceptProvider, Object: 199, Format String: <null>
'    2, 12, 199
'    
'    Provider: InterceptProvider, Object: 2, Format String: R
'    Provider: InterceptProvider, Object: 12, Format String: R
'    Provider: InterceptProvider, Object: 199, Format String: R
'    II, XII, CXCIX

字符串格式 Q &String.Format Q & A

为什么建议通过调用方法来插入字符串 String.Format ？Why do you recommend string interpolation over calls to the String.Format method?

字符串内插为：String interpolation is:

• 更灵活。More flexible. 它可用于任何字符串，无需调用支持复合格式设置的方法。It can be used in any string without requiring a call to a method that supports composite formatting. 否则，必须调用 Format 方法或支持复合格式设置的其他方法，如 Console.WriteLine 或 StringBuilder.AppendFormat 。Otherwise, you have to call the Format method or another method that supports composite formatting, such as Console.WriteLine or StringBuilder.AppendFormat.

• 可读性更强。More readable. 由于插入到字符串中的表达式出现在内插表达式中（而不是自变量列表中），因此，内插字符串的代码和读取更为容易。Because the expression to insert into a string appears in the interpolated expression rather than in a argument list, interpolated strings are far easier to code and to read. 由于其可读性更高，内插字符串不仅可以替换对复合格式方法的调用，还可以在字符串串联操作中使用，以生成更简洁简洁的代码。Because of their greater readability, interpolated strings can replace not only calls to composite format methods, but they can also be used in string concatenation operations to produce more concise, clearer code.

下面两个代码示例的比较说明了经营字符串连接和对复合格式设置方法的调用的内插字符串。A comparison of the following two code examples illustrates the superiority of interpolated strings over string concatenation and calls to composite formatting methods. 在下面的示例中，使用多个字符串串联操作会生成详细的代码和难于阅读的代码。The use of multiple string concatenation operations in the following example produces verbose and hard-to-read code.

  string[] names = { "Balto", "Vanya", "Dakota", "Samuel", "Koani", "Yiska", "Yuma" };
  string output = names[0] + ", " + names[1] + ", " + names[2] + ", " + 
                  names[3] + ", " + names[4] + ", " + names[5] + ", " + 
                  names[6];  

  output += "\n";  
  var date = DateTime.Now;
  output += String.Format("It is {0:t} on {0:d}. The day of the week is {1}.", 
                          date, date.DayOfWeek);
  Console.WriteLine(output);                           
  // The example displays the following output:
  //     Balto, Vanya, Dakota, Samuel, Koani, Yiska, Yuma
  //     It is 10:29 AM on 1/8/2018. The day of the week is Monday.

Module Example
   Public Sub Main()
      Dim names = { "Balto", "Vanya", "Dakota", "Samuel", "Koani", "Yiska", "Yuma" }
      Dim output = names(0) + ", " + names(1) + ", " + names(2) + ", " + 
                   names(3) + ", " + names(4) + ", " + names(5) + ", " + 
                   names(6)  
    
      output += vbCrLf  
      Dim dat = DateTime.Now
      output += String.Format("It is {0:t} on {0:d}. The day of the week is {1}.", 
                              dat, dat.DayOfWeek)
      Console.WriteLine(output)                           
   End Sub
End Module
' The example displays the following output:
'     Balto, Vanya, Dakota, Samuel, Koani, Yiska, Yuma
'     It is 10:29 AM on 1/8/2018. The day of the week is Monday.

与此相反，在下面的示例中使用内插字符串会生成比字符串串联语句更清晰、更简洁的代码，并对 Format 上一示例中的方法进行调用。In contrast, the use of interpolated strings in the following example produce much clearer, more concise code than the string concatenation statement and the call to the Format method in the previous example.

  string[] names = { "Balto", "Vanya", "Dakota", "Samuel", "Koani", "Yiska", "Yuma" };
  string output = $"{names[0]}, {names[1]}, {names[2]}, {names[3]}, {names[4]}, " + 
                  $"{names[5]}, {names[6]}";  

  var date = DateTime.Now;
  output += $"\nIt is {date:t} on {date:d}. The day of the week is {date.DayOfWeek}.";
  Console.WriteLine(output);                           
  // The example displays the following output:
  //     Balto, Vanya, Dakota, Samuel, Koani, Yiska, Yuma
  //     It is 10:29 AM on 1/8/2018. The day of the week is Monday.

Module Example
   Public Sub Main()
      Dim names = { "Balto", "Vanya", "Dakota", "Samuel", "Koani", "Yiska", "Yuma" }
      Dim output = $"{names(0)}, {names(1)}, {names(2)}, {names(3)}, {names(4)}, " + 
                   $"{names(5)}, {names(6)}"  
    
      Dim dat = DateTime.Now
      output += $"{vbCrLf}It is {dat:t} on {dat:d}. The day of the week is {dat.DayOfWeek}." 
      Console.WriteLine(output)                           
   End Sub
End Module
' The example displays the following output:
'     Balto, Vanya, Dakota, Samuel, Koani, Yiska, Yuma
'     It is 10:29 AM on 1/8/2018. The day of the week is Monday.

在哪里可以找到可用于格式项的预定义格式字符串列表？Where can I find a list of the predefined format strings that can be used with format items?

• 对于所有整型和浮点类型，请参阅 标准数字格式字符串 和 自定义数字格式字符串。For all integral and floating-point types, see Standard Numeric Format Strings and Custom Numeric Format Strings.

• 对于日期和时间值，请参阅 标准日期和时间格式字符串 和 自定义日期和时间格式字符串。For date and time values, see Standard Date and Time Format Strings and Custom Date and Time Format Strings.

• 对于枚举值，请参阅 枚举格式字符串。For enumeration values, see Enumeration Format Strings.

• 有关 TimeSpan 值，请参阅 标准 Timespan 格式字符串 和 自定义 timespan 格式字符串。For TimeSpan values, see Standard TimeSpan Format Strings and Custom TimeSpan Format Strings.

• 有关 Guid 值，请参阅引用页的 "备注" 部分 Guid.ToString(String) 。For Guid values, see the Remarks section of the Guid.ToString(String) reference page.

如何实现控制替换格式项的结果字符串的对齐方式吗？How do I control the alignment of the result strings that replace format items?

格式项的一般语法为：The general syntax of a format item is:

{index[,alignment][: formatString]}

其中， 对齐方式 是一个定义字段宽度的带符号整数。where alignment is a signed integer that defines the field width. 如果此值为负数，则字段中的文本为左对齐。If this value is negative, text in the field is left-aligned. 如果为正数，则文本右对齐。If it is positive, text is right-aligned.

如何实现控制小数点分隔符后的位数？How do I control the number of digits after the decimal separator?

除 "D" (之外的所有 标准数字格式字符串 （仅适用于整数) "G"、"R" 和 "X"）都允许使用精度说明符定义结果字符串中的小数位数。All standard numeric format strings except "D" (which is used with integers only), "G", "R", and "X" allow a precision specifier that defines the number of decimal digits in the result string. 下面的示例使用标准数字格式字符串来控制结果字符串中的小数位数。The following example uses standard numeric format strings to control the number of decimal digits in the result string.

object[] values = { 1603, 1794.68235, 15436.14 };
string result;
foreach (var value in values) {
   result = String.Format("{0,12:C2}   {0,12:E3}   {0,12:F4}   {0,12:N3}  {1,12:P2}\n",
                          Convert.ToDouble(value), Convert.ToDouble(value) / 10000);
   Console.WriteLine(result);
}                           
// The example displays output like the following:
//       $1,603.00     1.603E+003      1603.0000      1,603.000       16.03 %
//    
//       $1,794.68     1.795E+003      1794.6824      1,794.682       17.95 %
//    
//      $15,436.14     1.544E+004     15436.1400     15,436.140      154.36 %

Module Example
   Public Sub Main()
      Dim values() As Object = { 1603, 1794.68235, 15436.14 }
      Dim result As String
      For Each value In values
         result = String.Format("{0,12:C2}   {0,12:E3}   {0,12:F4}   {0,12:N3}  {1,12:P2}",
                                value, CDbl(value) / 10000)
         Console.WriteLine(result) 
         Console.WriteLine()
      Next                             
   End Sub
End Module
' The example displays the following output:
'       $1,603.00     1.603E+003      1603.0000      1,603.000       16.03 %
'    
'       $1,794.68     1.795E+003      1794.6824      1,794.682       17.95 %
'    
'      $15,436.14     1.544E+004     15436.1400     15,436.140      154.36 %

如果使用的是 自定义数字格式字符串，请使用 "0" 格式说明符控制结果字符串中的小数位数，如下面的示例所示。If you're using a custom numeric format string, use the "0" format specifier to control the number of decimal digits in the result string, as the following example shows.

decimal value = 16309.5436m;
string result = String.Format("{0,12:#.00000} {0,12:0,000.00} {0,12:000.00#}", 
                              value);
Console.WriteLine(result);
// The example displays the following output:
//        16309.54360    16,309.54    16309.544

Module Example
   Public Sub Main()
      Dim value As Decimal = 16309.5436d
      Dim result As String = String.Format("{0,12:#.00000} {0,12:0,000.00} {0,12:000.00#}", 
                                           value)
      Console.WriteLine(result)
   End Sub
End Module
' The example displays the following output:
'    16309.54360    16,309.54    16309.544

如何实现控制整数位数？How do I control the number of integral digits?

默认情况下，格式设置操作仅显示非零整数位数。By default, formatting operations only display non-zero integral digits. 如果要设置整数格式，则可以使用带有 "D" 和 "X" 标准格式字符串的精度说明符来控制数字的位数。If you are formatting integers, you can use a precision specifier with the "D" and "X" standard format strings to control the number of digits.

int value = 1326;
string result = String.Format("{0,10:D6} {0,10:X8}", value);
Console.WriteLine(result);
// The example displays the following output:
//     001326   0000052E

Module Example
   Public Sub Main()
      Dim value As Integer = 1326
      Dim result As String = String.Format("{0,10:D6} {0,10:X8}", value)
      Console.WriteLine(result)
   End Sub
End Module
' The example displays the following output:
'       001326   0000052E

可以通过使用 "0" 自定义数值格式说明符，使用前导零填充整数或浮点数，以生成具有指定数量整数位数的结果字符串，如下面的示例所示。You can pad an integer or floating-point number with leading zeros to produce a result string with a specified number of integral digits by using the "0" custom numeric format specifier, as the following example shows.

int value = 16342;
string result = String.Format("{0,18:00000000} {0,18:00000000.000} {0,18:000,0000,000.0}", 
                              value);
Console.WriteLine(result);
// The example displays the following output:
//           00016342       00016342.000    0,000,016,342.0

Module Example
   Public Sub Main()
      Dim value As Integer = 16342
      Dim result As String = String.Format("{0,18:00000000} {0,18:00000000.000} {0,18:000,0000,000.0}", 
                                           value)
      Console.WriteLine(result)
   End Sub
End Module
' The example displays the following output:
'           00016342       00016342.000    0,000,016,342.0

可以在 "格式" 列表中包含多少项？How many items can I include in the format list?

没有实际限制。There is no practical limit. 方法的第二个参数 Format(IFormatProvider, String, Object[]) 使用特性进行标记 ParamArrayAttribute ，这允许您将分隔的列表或对象数组作为格式列表包括在内。The second parameter of the Format(IFormatProvider, String, Object[]) method is tagged with the ParamArrayAttribute attribute, which allows you to include either a delimited list or an object array as your format list.

如何实现在结果字符串中包含 "{" 和 "}" ( 文本大括号 ) How do I include literal braces ("{" and "}") in the result string?

例如，如何防止下面的方法调用引发 FormatException 异常？For example, how do you prevent the following method call from throwing a FormatException exception?

result = String.Format("The text has {0} '{' characters and {1} '}' characters.",
                       nOpen, nClose);

result = String.Format("The text has {0} '{' characters and {1} '}' characters.",
                       nOpen, nClose)

单个左大括号或右大括号始终解释为格式项的开头或结尾。A single opening or closing brace is always interpreted as the beginning or end of a format item. 若要按原义解释，则必须对其进行转义。To be interpreted literally, it must be escaped. 通过添加另一个大括号 ( "{{" 和 "}}" 而不是 "{" 和 "}" ) 来转义大括号，如以下方法调用所示：You escape a brace by adding another brace ("{{" and "}}" instead of "{" and "}"), as in the following method call:

string result;
int nOpen = 1;
int nClose = 2;
result = String.Format("The text has {0} '{{' characters and {1} '}}' characters.",
                       nOpen, nClose);
Console.WriteLine(result);

result = String.Format("The text has {0} '{{' characters and {1} '}}' characters.",
                       nOpen, nClose)

不过，甚至可以轻松地误解转义大括号。However, even escaped braces are easily misinterpreted. 建议在格式列表中包含大括号，并使用格式项将它们插入到结果字符串中，如下面的示例所示。We recommend that you include braces in the format list and use format items to insert them in the result string, as the following example shows.

string result;
int nOpen = 1;
int nClose = 2;
result = String.Format("The text has {0} '{1}' characters and {2} '{3}' characters.",
                       nOpen, "{", nClose, "}");
Console.WriteLine(result);

result = String.Format("The text has {0} '{1}' characters and {2} '{3}' characters.",
                       nOpen, "{", nClose, "}")

为什么调用字符串。 Format 方法会引发 FormatException？Why does my call to the String.Format method throw a FormatException?

最常见的原因是，格式项的索引不与 "格式" 列表中的对象相对应。The most common cause of the exception is that the index of a format item doesn't correspond to an object in the format list. 通常，这表示您已 misnumbered 格式项的索引，或者您忘记在 "格式" 列表中包含一个对象。Usually this indicates that you've misnumbered the indexes of format items or you've forgotten to include an object in the format list. 尝试包含非转义的左大括号或右大括号会引发 FormatException 。Attempting to include an unescaped left or right brace character also throws a FormatException. 偶尔，异常是由键入错误引起的;例如，典型的错误是错误地键入了 "[" (左括号) 而不是 "{" (左大括号) 。Occasionally, the exception is the result of a typo; for example, a typical mistake is to mistype "[" (the left bracket) instead of "{" (the left brace).

如果 (IFormatProvider，System.string，system.object [] ) 方法的格式支持参数数组，则我的代码在使用数组时为什么会引发异常？If the Format(System.IFormatProvider,System.String,System.Object[]) method supports parameter arrays, why does my code throw an exception when I use an array?

例如，以下代码将引发 FormatException 异常：For example, the following code throws a FormatException exception:

Random rnd = new Random();
int[]  numbers = new int[4];
int total = 0;
for (int ctr = 0; ctr <= 2; ctr++) {
   int number = rnd.Next(1001);
   numbers[ctr] = number;
   total += number;
}   
numbers[3] = total;
Console.WriteLine("{0} + {1} + {2} = {3}", numbers);   

Imports System.Collections.Generic

Module Example
   Public Sub Main()
      Dim rnd As New Random()
      Dim numbers(3) As Integer
      Dim total As Integer = 0
      For ctr = 0 To 2
         Dim number As Integer = rnd.Next(1001)
         numbers(ctr) = number
         total += number
      Next
      numbers(3) = total
      Console.WriteLine("{0} + {1} + {2} = {3}", numbers)   
   End Sub
End Module

这是编译器重载决策的问题。This is a problem of compiler overload resolution. 由于编译器无法将整数数组转换为对象数组，因此它将整数数组视为单个参数，因此它将调用 Format(String, Object) 方法。Because the compiler cannot convert an array of integers to an object array, it treats the integer array as a single argument, so it calls the Format(String, Object) method. 引发此异常的原因是存在四个格式项，但在 "格式" 列表中只有一个项。The exception is thrown because there are four format items but only a single item in the format list.

因为 Visual Basic 和 c # 都不能将整数数组转换为对象数组，所以必须在调用方法之前自行执行转换 Format(String, Object[]) 。Because neither Visual Basic nor C# can convert an integer array to an object array, you have to perform the conversion yourself before calling the Format(String, Object[]) method. 以下示例提供了一个实现。The following example provides one implementation.

Random rnd = new Random();
int[]  numbers = new int[4];
int total = 0;
for (int ctr = 0; ctr <= 2; ctr++) {
   int number = rnd.Next(1001);
   numbers[ctr] = number;
   total += number;
}   
numbers[3] = total;
object[] values = new object[numbers.Length];
numbers.CopyTo(values, 0);
Console.WriteLine("{0} + {1} + {2} = {3}", values);   

Imports System.Collections.Generic

Module Example
   Public Sub Main()
      Dim rnd As New Random()
      Dim numbers(3) As Integer
      Dim total As Integer = 0
      For ctr = 0 To 2
         Dim number As Integer = rnd.Next(1001)
         numbers(ctr) = number
         total += number
      Next
      numbers(3) = total
      Dim values(numbers.Length - 1) As Object
      numbers.CopyTo(values, 0) 
      Console.WriteLine("{0} + {1} + {2} = {3}", values)   
   End Sub
End Module

public:
 static System::String ^ Format(System::String ^ format, System::Object ^ arg0);

public static string Format (string format, object arg0);

public static string Format (string format, object? arg0);

static member Format : string * obj -> string

Public Shared Function Format (format As String, arg0 As Object) As String

using namespace System;

void main()
{
   DateTime birthdate = DateTime(1993, 7, 28);
   array<DateTime>^ dates = gcnew array<DateTime> { DateTime(1993, 8, 16), 
                                                    DateTime(1994, 7, 28), 
                                                    DateTime(2000, 10, 16), 
                                                    DateTime(2003, 7, 27), 
                                                    DateTime(2007, 5, 27) };

   for each (DateTime dateValue in dates)
   {
      TimeSpan interval = dateValue - birthdate;
      // Get the approximate number of years, without accounting for leap years.
      int years = ((int)interval.TotalDays) / 365;
      // See if adding the number of years exceeds dateValue.
      String^ output;
      if (birthdate.AddYears(years) <= dateValue) {
         output = String::Format("You are now {0} years old.", years);
         Console::WriteLine(output);
      }   
      else {
         output = String::Format("You are now {0} years old.", years - 1);
         Console::WriteLine(output);
      }      
   }
}
// The example displays the following output:
//       You are now 0 years old.
//       You are now 1 years old.
//       You are now 7 years old.
//       You are now 9 years old.
//       You are now 13 years old.

DateTime birthdate = new DateTime(1993, 7, 28);
DateTime[] dates = { new DateTime(1993, 8, 16), 
                     new DateTime(1994, 7, 28), 
                     new DateTime(2000, 10, 16), 
                     new DateTime(2003, 7, 27), 
                     new DateTime(2007, 5, 27) };

foreach (DateTime dateValue in dates)
{
   TimeSpan interval = dateValue - birthdate;
   // Get the approximate number of years, without accounting for leap years.
   int years = ((int) interval.TotalDays) / 365;
   // See if adding the number of years exceeds dateValue.
   string output;
   if (birthdate.AddYears(years) <= dateValue) {
      output = String.Format("You are now {0} years old.", years);
      Console.WriteLine(output);
   }   
   else {
      output = String.Format("You are now {0} years old.", years - 1);
      Console.WriteLine(output);
   }      
}
// The example displays the following output:
//       You are now 0 years old.
//       You are now 1 years old.
//       You are now 7 years old.
//       You are now 9 years old.
//       You are now 13 years old.

Module Example
   Public Sub Main()
      Dim birthdate As Date = #7/28/1993#
      Dim dates() As Date = { #9/16/1993#, #7/28/1994#, #10/16/2000#, _
                              #7/27/2003#, #5/27/2007# }
      For Each dateValue As Date In dates
         Dim interval As TimeSpan = dateValue - birthdate
         ' Get the approximate number of years, without accounting for leap years.
         Dim years As Integer = CInt(interval.TotalDays) \ 365
         ' See if adding the number of years exceeds dateValue.
         Dim output As String
         If birthdate.AddYears(years) <= dateValue Then
            output = String.Format("You are now {0} years old.", years)
            Console.WriteLine(output)
         Else
            output = String.Format("You are now {0} years old.", years - 1)
            Console.WriteLine(output)   
         End If
      Next
   End Sub
End Module
' The example displays the following output:
'       You are now 0 years old.
'       You are now 1 years old.
'       You are now 7 years old.
'       You are now 9 years old.
'       You are now 13 years old.

public:
 static System::String ^ Format(System::String ^ format, ... cli::array <System::Object ^> ^ args);

public static string Format (string format, params object[] args);

public static string Format (string format, params object?[] args);

static member Format : string * obj[] -> string

Public Shared Function Format (format As String, ParamArray args As Object()) As String

using namespace System;

void main()
{
   DateTime date1 = DateTime(2009, 7, 1);
   TimeSpan hiTime = TimeSpan(14, 17, 32);
   Decimal hiTemp = (Decimal) 62.1; 
   TimeSpan loTime = TimeSpan(3, 16, 10);
   Decimal loTemp = (Decimal)54.8; 

   String^ result1 = String::Format("Temperature on {0:d}:\n{1,11}: {2} degrees (hi)\n{3,11}: {4} degrees (lo)", 
                                    date1, hiTime, hiTemp, loTime, loTemp);
   Console::WriteLine(result1);
   Console::WriteLine();
           
   String^ result2 = String::Format("Temperature on {0:d}:\n{1,11}: {2} degrees (hi)\n{3,11}: {4} degrees (lo)", 
                                    gcnew array<Object^> { date1, hiTime, hiTemp, loTime, loTemp });
   Console::WriteLine(result2);
}
// The example displays the following output:
//       Temperature on 7/1/2009:
//          14:17:32: 62.1 degrees (hi)
//          03:16:10: 54.8 degrees (lo)
//       Temperature on 7/1/2009:
//          14:17:32: 62.1 degrees (hi)
//          03:16:10: 54.8 degrees (lo)

DateTime date1 = new DateTime(2009, 7, 1);
TimeSpan hiTime = new TimeSpan(14, 17, 32);
decimal hiTemp = 62.1m; 
TimeSpan loTime = new TimeSpan(3, 16, 10);
decimal loTemp = 54.8m; 

string result1 = String.Format("Temperature on {0:d}:\n{1,11}: {2} degrees (hi)\n{3,11}: {4} degrees (lo)", 
                               date1, hiTime, hiTemp, loTime, loTemp);
Console.WriteLine(result1);
Console.WriteLine();
     
string result2 = String.Format("Temperature on {0:d}:\n{1,11}: {2} degrees (hi)\n{3,11}: {4} degrees (lo)", 
                               new object[] { date1, hiTime, hiTemp, loTime, loTemp });
Console.WriteLine(result2);
// The example displays output like the following:
//       Temperature on 7/1/2009:
//          14:17:32: 62.1 degrees (hi)
//          03:16:10: 54.8 degrees (lo)
//       Temperature on 7/1/2009:
//          14:17:32: 62.1 degrees (hi)
//          03:16:10: 54.8 degrees (lo)

Module Example
   Public Sub Main()
      Dim date1 As Date = #7/1/2009#
      Dim hiTime As New TimeSpan(14, 17, 32)
      Dim hiTemp As Decimal = 62.1d 
      Dim loTime As New TimeSpan(3, 16, 10)
      Dim loTemp As Decimal = 54.8d 

      Dim result1 As String = String.Format("Temperature on {0:d}:{5}{1,11}: {2} degrees (hi){5}{3,11}: {4} degrees (lo)", _
                                           date1, hiTime, hiTemp, loTime, loTemp, vbCrLf)
      Console.WriteLine(result1)
      Console.WriteLine()
           
      Dim result2 As String = String.Format("Temperature on {0:d}:{5}{1,11}: {2} degrees (hi){5}{3,11}: {4} degrees (lo)", _
                                            New Object() { date1, hiTime, hiTemp, loTime, loTemp, vbCrLf })
      Console.WriteLine(result2)                                            
   End Sub
End Module
' The example displays the following output:
'       Temperature on 7/1/2009:
'          14:17:32: 62.1 degrees (hi)
'          03:16:10: 54.8 degrees (lo)
'
'       Temperature on 7/1/2009:
'          14:17:32: 62.1 degrees (hi)
'          03:16:10: 54.8 degrees (lo)

using namespace System;

ref class CityInfo
{
public:
   CityInfo(String^ name, int population, Decimal area, int year)
   {
      this->Name = name;
      this->Population = population;
      this->Area = area;
      this->Year = year;
   }
   
   String^ Name; 
   int Population;
   Decimal Area;
   int Year;
};

ref class Example
{
public:
   static void ShowPopulationData(CityInfo^ city)
   {
      array<Object^>^ args = gcnew array<Object^> { city->Name, city->Year, city->Population, city->Area };
      String^ result = String::Format("{0} in {1}: Population {2:N0}, Area {3:N1} sq. feet", 
                                    args);
      Console::WriteLine(result); 
   }
};

void main()
{
   CityInfo^ nyc2010 = gcnew CityInfo("New York", 8175133, (Decimal) 302.64, 2010);
   Example::ShowPopulationData(nyc2010);
   CityInfo^ sea2010 = gcnew CityInfo("Seattle", 608660, (Decimal) 83.94, 2010);      
   Example::ShowPopulationData(sea2010); 
}
// The example displays the following output:
//       New York in 2010: Population 8,175,133, Area 302.6 sq. feet
//       Seattle in 2010: Population 608,660, Area 83.9 sq. feet

using System;

public class CityInfo
{
   public CityInfo(String name, int population, Decimal area, int year)
   {
      this.Name = name;
      this.Population = population;
      this.Area = area;
      this.Year = year;
   }
   
   public readonly String Name; 
   public readonly int Population;
   public readonly Decimal Area;
   public readonly int Year;
}

public class Example
{
   public static void Main()
   {
      CityInfo nyc2010 = new CityInfo("New York", 8175133, 302.64m, 2010);
      ShowPopulationData(nyc2010);
      CityInfo sea2010 = new CityInfo("Seattle", 608660, 83.94m, 2010);      
      ShowPopulationData(sea2010); 
   }

   private static void ShowPopulationData(CityInfo city)
   {
      object[] args = { city.Name, city.Year, city.Population, city.Area };
      String result = String.Format("{0} in {1}: Population {2:N0}, Area {3:N1} sq. feet", 
                                    args);
      Console.WriteLine(result); 
   }
}
// The example displays the following output:
//       New York in 2010: Population 8,175,133, Area 302.6 sq. feet
//       Seattle in 2010: Population 608,660, Area 83.9 sq. feet

Public Class CityInfo
   Public Sub New(name As String, population As Integer, area As Decimal, year As Integer)
      Me.Name = name
      Me.Population = population
      Me.Area = area
      Me.Year = year
   End Sub
   
   Public ReadOnly Name As String
   Public ReadOnly Population As Integer
   Public ReadOnly Area As Decimal
   Public ReadOnly Year As Integer
End Class

Module Example
   Public Sub Main()
      Dim nyc2010 As New CityInfo("New York", 8175133, 302.64d, 2010)
      ShowPopulationData(nyc2010)
      Dim sea2010 As New CityInfo("Seattle", 608660, 83.94d, 2010)      
      ShowPopulationData(sea2010) 
   End Sub
   
   Private Sub ShowPopulationData(city As CityInfo)
      Dim args() As Object = { city.Name, city.Year, city.Population, city.Area }
      Dim result = String.Format("{0} in {1}: Population {2:N0}, Area {3:N1} sq. feet", args)
      Console.WriteLine(result) 
   End Sub
End Module
' The example displays the following output:
'       New York in 2010: Population 8,175,133, Area 302.6 sq. feet
'       Seattle in 2010: Population 608,660, Area 83.9 sq. feet

public:
 static System::String ^ Format(IFormatProvider ^ provider, System::String ^ format, System::Object ^ arg0);

public static string Format (IFormatProvider provider, string format, object arg0);

public static string Format (IFormatProvider? provider, string format, object? arg0);

static member Format : IFormatProvider * string * obj -> string

Public Shared Function Format (provider As IFormatProvider, format As String, arg0 As Object) As String

public:
 static System::String ^ Format(IFormatProvider ^ provider, System::String ^ format, ... cli::array <System::Object ^> ^ args);

public static string Format (IFormatProvider provider, string format, params object[] args);

public static string Format (IFormatProvider? provider, string format, params object?[] args);

static member Format : IFormatProvider * string * obj[] -> string

Public Shared Function Format (provider As IFormatProvider, format As String, ParamArray args As Object()) As String

string[] cultureNames = { "en-US", "fr-FR", "de-DE", "es-ES" };

DateTime dateToDisplay = new DateTime(2009, 9, 1, 18, 32, 0);
double value = 9164.32;

Console.WriteLine("Culture     Date                                Value\n");
foreach (string cultureName in cultureNames)
{
   System.Globalization.CultureInfo culture = new System.Globalization.CultureInfo(cultureName);
   string output = String.Format(culture, "{0,-11} {1,-35:D} {2:N}", 
                                 culture.Name, dateToDisplay, value);
   Console.WriteLine(output);
}    
// The example displays the following output:
//    Culture     Date                                Value
//    
//    en-US       Tuesday, September 01, 2009         9,164.32
//    fr-FR       mardi 1 septembre 2009              9 164,32
//    de-DE       Dienstag, 1. September 2009         9.164,32
//    es-ES       martes, 01 de septiembre de 2009    9.164,32

Imports System.Globalization

Module Example
   Public Sub Main()
      Dim cultureNames() As String = { "en-US", "fr-FR", "de-DE", "es-ES" }
      
      Dim dateToDisplay As Date = #9/1/2009 6:32PM#
      Dim value As Double = 9164.32

      Console.WriteLine("Culture     Date                                Value")
      Console.WriteLine()      
      For Each cultureName As String In cultureNames
         Dim culture As New CultureInfo(cultureName)
         Dim output As String = String.Format(culture, "{0,-11} {1,-35:D} {2:N}", _
                                              culture.Name, dateToDisplay, value)
         Console.WriteLine(output)
      Next    
   End Sub
End Module
' The example displays the following output:
'       Culture     Date                                Value
'       
'       en-US       Tuesday, September 01, 2009         9,164.32
'       fr-FR       mardi 1 septembre 2009              9 164,32
'       de-DE       Dienstag, 1. September 2009         9.164,32
'       es-ES       martes, 01 de septiembre de 2009    9.164,32

public:
 static System::String ^ Format(System::String ^ format, System::Object ^ arg0, System::Object ^ arg1);

public static string Format (string format, object arg0, object arg1);

public static string Format (string format, object? arg0, object? arg1);

static member Format : string * obj * obj -> string

Public Shared Function Format (format As String, arg0 As Object, arg1 As Object) As String

using namespace System;
using namespace System::Collections::Generic;

void main()
{
   Dictionary<DateTime, Double>^ temperatureInfo = gcnew Dictionary<DateTime, Double>(); 
   temperatureInfo->Add(DateTime(2010, 6, 1, 14, 0, 0), 87.46);
   temperatureInfo->Add(DateTime(2010, 12, 1, 10, 0, 0), 36.81);
      
   Console::WriteLine("Temperature Information:\n");
   String^ output;   
   for each (KeyValuePair<DateTime, Double>^ item in temperatureInfo)
   {
      output = String::Format("Temperature at {0,8:t} on {0,9:d}: {1,5:N1}�F", 
                              item->Key, item->Value);
      Console::WriteLine(output);
   }
}
// The example displays the following output:
//       Temperature Information:
//       
//       Temperature at  2:00 PM on  6/1/2010:  87.5�F
//       Temperature at 10:00 AM on 12/1/2010:  36.8�F

Dictionary<DateTime, Double> temperatureInfo = new Dictionary<DateTime, Double>(); 
temperatureInfo.Add(new DateTime(2010, 6, 1, 14, 0, 0), 87.46);
temperatureInfo.Add(new DateTime(2010, 12, 1, 10, 0, 0), 36.81);

Console.WriteLine("Temperature Information:\n");
string output;   
foreach (var item in temperatureInfo)
{
   output = String.Format("Temperature at {0,8:t} on {0,9:d}: {1,5:N1}°F", 
                          item.Key, item.Value);
   Console.WriteLine(output);
}
// The example displays output like the following:
//       Temperature Information:
//       
//       Temperature at  2:00 PM on  6/1/2010:  87.5°F
//       Temperature at 10:00 AM on 12/1/2010:  36.8°F

Imports System.Collections.Generic

Module Example
   Public Sub Main()
      Dim temperatureInfo As New Dictionary(Of Date, Double) 
      temperatureInfo.Add(#6/1/2010 2:00PM#, 87.46)
      temperatureInfo.Add(#12/1/2010 10:00AM#, 36.81)
      
      Console.WriteLine("Temperature Information:")
      Console.WriteLine()
      Dim output As String   
      For Each item In temperatureInfo
         output = String.Format("Temperature at {0,8:t} on {0,9:d}: {1,5:N1}°F", _
                                item.Key, item.Value)
         Console.WriteLine(output)
      Next
   End Sub
End Module
' The example displays the following output:
'       Temperature Information:
'       
'       Temperature at  2:00 PM on  6/1/2010:  87.5°F
'       Temperature at 10:00 AM on 12/1/2010:  36.8°F

public:
 static System::String ^ Format(IFormatProvider ^ provider, System::String ^ format, System::Object ^ arg0, System::Object ^ arg1);

public static string Format (IFormatProvider provider, string format, object arg0, object arg1);

public static string Format (IFormatProvider? provider, string format, object? arg0, object? arg1);

static member Format : IFormatProvider * string * obj * obj -> string

Public Shared Function Format (provider As IFormatProvider, format As String, arg0 As Object, arg1 As Object) As String

public:
 static System::String ^ Format(System::String ^ format, System::Object ^ arg0, System::Object ^ arg1, System::Object ^ arg2);

public static string Format (string format, object arg0, object arg1, object arg2);

public static string Format (string format, object? arg0, object? arg1, object? arg2);

static member Format : string * obj * obj * obj -> string

Public Shared Function Format (format As String, arg0 As Object, arg1 As Object, arg2 As Object) As String

using namespace System;

void main()
{
   String^ formatString = "    {0,10} ({0,8:X8})\n" + 
                           "And {1,10} ({1,8:X8})\n" + 
                           "  = {2,10} ({2,8:X8})";
   int value1 = 16932;
   int value2 = 15421;
   String^ result = String::Format(formatString, 
                                   value1, value2, value1 & value2);
   Console::WriteLine(result);
}
// The example displays the following output:
//                16932 (00004224)
//       And      15421 (00003C3D)
//         =         36 (00000024)

string formatString = "    {0,10} ({0,8:X8})\n" + 
                      "And {1,10} ({1,8:X8})\n" + 
                      "  = {2,10} ({2,8:X8})";
int value1 = 16932;
int value2 = 15421;
string result = String.Format(formatString, 
                              value1, value2, value1 & value2);
Console.WriteLine(result);
// The example displays the following output:
//                16932 (00004224)
//       And      15421 (00003C3D)
//         =         36 (00000024)

Public Module Example
   Public Sub Main()
      Dim formatString As String = "    {0,10} ({0,8:X8})" + vbCrLf +  _
                                   "And {1,10} ({1,8:X8})" + vbCrLf + _
                                   "  = {2,10} ({2,8:X8})"
      Dim value1 As Integer = 16932
      Dim value2 As Integer = 15421
      Dim result As String = String.Format(formatString, _
                                           value1, value2, value1 And value2)
      Console.WriteLine(result)                          
   End Sub
End Module
' The example displays the following output:
'                16932 (00004224)
'       And      15421 (00003C3D)
'         =         36 (00000024)

public:
 static System::String ^ Format(IFormatProvider ^ provider, System::String ^ format, System::Object ^ arg0, System::Object ^ arg1, System::Object ^ arg2);

public static string Format (IFormatProvider provider, string format, object arg0, object arg1, object arg2);

public static string Format (IFormatProvider? provider, string format, object? arg0, object? arg1, object? arg2);

static member Format : IFormatProvider * string * obj * obj * obj -> string

Public Shared Function Format (provider As IFormatProvider, format As String, arg0 As Object, arg1 As Object, arg2 As Object) As String