String.TrimStart 方法
定義
重要
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多載
TrimStart() |
移除目前字串開頭的所有空白字元。 |
TrimStart(Char) |
移除出現在目前字串開頭的所有指定字元。 |
TrimStart(Char[]) |
移除出現在目前字串開頭的所有陣列指定字元集。 |
TrimStart()
- Source:
- String.Manipulation.cs
- Source:
- String.Manipulation.cs
- Source:
- String.Manipulation.cs
移除目前字串開頭的所有空白字元。
public:
System::String ^ TrimStart();
public string TrimStart ();
member this.TrimStart : unit -> string
Public Function TrimStart () As String
傳回
從目前字串開頭移除所有空白字元後,遺留下來的字串。 如果在目前的執行個體中無法修剪任何字元,則方法傳回未變更的目前執行個體。
備註
方法 TrimStart
會從目前字串中移除所有前置空白字元。 遇到非空白字元時,修剪作業會停止。 例如,如果目前的字串是 「abc xyz 」,則 TrimStart
方法會傳回 「abc xyz 」。
注意
TrimStart
如果方法從目前實例移除任何字元,這個方法就不會修改目前實例的值。 相反地,它會傳回新的字串,其中會移除目前實例中找到的所有前置空白字元。
適用於
TrimStart(Char)
- Source:
- String.Manipulation.cs
- Source:
- String.Manipulation.cs
- Source:
- String.Manipulation.cs
移除出現在目前字串開頭的所有指定字元。
public:
System::String ^ TrimStart(char trimChar);
public string TrimStart (char trimChar);
member this.TrimStart : char -> string
Public Function TrimStart (trimChar As Char) As String
參數
- trimChar
- Char
要移除的 Unicode 字元。
傳回
從目前字串開頭移除所有出現的 trimChar
字元後,遺留下來的字串。 如果在目前的執行個體中無法修剪任何字元,則方法傳回未變更的目前執行個體。
備註
方法 TrimStart(System.Char)
會從目前字串中移除所有前置 trimChar
字元。 修剪作業會在遇到未 trimChar
遇到的字元時停止。 例如,如果 is trimChar
-
且目前的字串為 「---abc---xyz----」,則 TrimStart(System.Char)
方法會傳回 「abc---xyz----」。
注意
TrimStart(System.Char)
如果方法從目前實例移除任何字元,這個方法就不會修改目前實例的值。 相反地,它會傳回新的字串,其中會移除目前實例中找到的所有前置 trimChar
字元。
適用於
TrimStart(Char[])
- Source:
- String.Manipulation.cs
- Source:
- String.Manipulation.cs
- Source:
- String.Manipulation.cs
移除出現在目前字串開頭的所有陣列指定字元集。
public:
System::String ^ TrimStart(... cli::array <char> ^ trimChars);
public string TrimStart (params char[] trimChars);
public string TrimStart (params char[]? trimChars);
member this.TrimStart : char[] -> string
Public Function TrimStart (ParamArray trimChars As Char()) As String
參數
- trimChars
- Char[]
要移除的 Unicode 字元陣列或 null
。
傳回
從目前的字串開頭處移除 trimChars
參數中所有出現的字元後,所保留下來的字串。 如果 trimChars
是 null
或空陣列,則反而會移除空白字元。 如果在目前的執行個體中無法修剪任何字元,則方法傳回未變更的目前執行個體。
範例
下列範例示範 方法的基本功能 TrimStart :
// TrimStart examples
string lineWithLeadingSpaces = " Hello World!";
string lineWithLeadingSymbols = "$$$$Hello World!";
string lineWithLeadingUnderscores = "_____Hello World!";
string lineWithLeadingLetters = "xxxxHello World!";
string lineAfterTrimStart = string.Empty;
// Make it easy to print out and work with all of the examples
string[] lines = { lineWithLeadingSpaces, lineWithLeadingSymbols, lineWithLeadingUnderscores, lineWithLeadingLetters };
foreach (var line in lines)
{
Console.WriteLine($"This line has leading characters: {line}");
}
// Output:
// This line has leading characters: Hello World!
// This line has leading characters: $$$$Hello World!
// This line has leading characters: _____Hello World!
// This line has leading characters: xxxxHello World!
// A basic demonstration of TrimStart in action
lineAfterTrimStart = lineWithLeadingSpaces.TrimStart(' ');
Console.WriteLine($"This is the result after calling TrimStart: {lineAfterTrimStart}");
// This is the result after calling TrimStart: Hello World!
// Since TrimStart accepts a character array of leading items to be removed as an argument,
// it's possible to do things like trim multiple pieces of data that each have different
// leading characters,
foreach (var lineToEdit in lines)
{
Console.WriteLine(lineToEdit.TrimStart(' ', '$', '_', 'x'));
}
// Result for each: Hello World!
// or handle pieces of data that have multiple kinds of leading characters
var lineToBeTrimmed = "__###__ John Smith";
lineAfterTrimStart = lineToBeTrimmed.TrimStart('_', '#', ' ');
Console.WriteLine(lineAfterTrimStart);
// Result: John Smith
// TrimStart examples
let lineWithLeadingSpaces = " Hello World!"
let lineWithLeadingSymbols = "$$$$Hello World!"
let lineWithLeadingUnderscores = "_____Hello World!"
let lineWithLeadingLetters = "xxxxHello World!"
// Make it easy to print out and work with all of the examples
let lines = [| lineWithLeadingSpaces; lineWithLeadingSymbols; lineWithLeadingUnderscores; lineWithLeadingLetters |]
for line in lines do
printfn $"This line has leading characters: {line}"
// Output:
// This line has leading characters: Hello World!
// This line has leading characters: $$$$Hello World!
// This line has leading characters: _____Hello World!
// This line has leading characters: xxxxHello World!
// A basic demonstration of TrimStart in action
let lineAfterTrimStart = lineWithLeadingSpaces.TrimStart ' '
printfn $"This is the result after calling TrimStart: {lineAfterTrimStart}"
// This is the result after calling TrimStart: Hello World!
// Since TrimStart accepts a character array of leading items to be removed as an argument,
// it's possible to do things like trim multiple pieces of data that each have different
// leading characters,
for lineToEdit in lines do
printfn $"""{lineToEdit.TrimStart(' ', '$', '_', 'x')}"""
// Result for each: Hello World!
// or handle pieces of data that have multiple kinds of leading characters
let lineToBeTrimmed = "__###__ John Smith"
let lineAfterTrimStart2 = lineToBeTrimmed.TrimStart('_', '#', ' ')
printfn $"{lineAfterTrimStart2}"
// Result: John Smith
Public Sub Main()
' TrimStart Examples
Dim lineWithLeadingSpaces as String = " Hello World!"
Dim lineWithLeadingSymbols as String = "$$$$Hello World!"
Dim lineWithLeadingUnderscores as String = "_____Hello World!"
Dim lineWithLeadingLetters as String = "xxxxHello World!"
Dim lineAfterTrimStart = String.Empty
' Make it easy to print out and work with all of the examples
Dim lines As String() = { lineWithLeadingSpaces, line lineWithLeadingSymbols, lineWithLeadingUnderscores, lineWithLeadingLetters }
For Each line As String in lines
Console.WriteLine($"This line has leading characters: {line}")
Next
' Output:
' This line has leading characters: Hello World!
' This line has leading characters: $$$$Hello World!
' This line has leading characters: _____Hello World!
' This line has leading characters: xxxxHello World!
Console.WriteLine($"This line has leading spaces: {lineWithLeadingSpaces}")
' This line has leading spaces: Hello World!
' A basic demonstration of TrimStart in action
lineAfterTrimStart = lineWithLeadingSpaces.TrimStart(" "c)
Console.WriteLine($"This is the result after calling TrimStart: {lineAfterTrimStart}")
' This is the result after calling TrimStart: Hello World!
' Since TrimStart accepts a character array of leading items to be removed as an argument,
' it's possible to do things like trim multiple pieces of data that each have different
' leading characters,
For Each lineToEdit As String in lines
Console.WriteLine(lineToEdit.TrimStart(" "c, "$"c, "_"c, "x"c ))
Next
' Result for each: Hello World!
' or handle pieces of data that have multiple kinds of leading characters
Dim lineToBeTrimmed as String = "__###__ John Smith"
lineAfterTrimStart = lineToBeTrimmed.TrimStart("_"c , "#"c , " "c)
Console.WriteLine(lineAfterTrimStart)
' Result: John Smith
End Sub
下列範例會 TrimStart 使用 方法來修剪源程式碼的空白字元和批註字元。 方法 StripComments
會包裝對 的呼叫 TrimStart ,並將包含空格和批註字元的字元陣列傳遞給它,這是 Visual Basic 中的單引號 ( ' ) ,以及 C# 或 F# 中的斜線 (/ ) 。 評估 TrimStart 字串是否為批註時,也會呼叫 方法來移除前置空白字元。
public static string[] StripComments(string[] lines)
{
List<string> lineList = new List<string>();
foreach (string line in lines)
{
if (line.TrimStart(' ').StartsWith("//"))
lineList.Add(line.TrimStart(' ', '/'));
}
return lineList.ToArray();
}
let stripComments (lines: #seq<string>) =
[| for line in lines do
if line.TrimStart(' ').StartsWith "//" then
line.TrimStart(' ', '/') |]
Public Shared Function StripComments(lines() As String) As String()
Dim lineList As New List(Of String)
For Each line As String In lines
If line.TrimStart(" "c).StartsWith("'") Then
linelist.Add(line.TrimStart("'"c, " "c))
End If
Next
Return lineList.ToArray()
End Function
下列範例說明如何呼叫 StripComments
方法。
public static void Main()
{
string[] lines = {"using System;",
"",
"public class HelloWorld",
"{",
" public static void Main()",
" {",
" // This code displays a simple greeting",
" // to the console.",
" Console.WriteLine(\"Hello, World.\");",
" }",
"}"};
Console.WriteLine("Before call to StripComments:");
foreach (string line in lines)
Console.WriteLine(" {0}", line);
string[] strippedLines = StripComments(lines);
Console.WriteLine("After call to StripComments:");
foreach (string line in strippedLines)
Console.WriteLine(" {0}", line);
}
// This code produces the following output to the console:
// Before call to StripComments:
// using System;
//
// public class HelloWorld
// {
// public static void Main()
// {
// // This code displays a simple greeting
// // to the console.
// Console.WriteLine("Hello, World.");
// }
// }
// After call to StripComments:
// This code displays a simple greeting
// to the console.
let lines =
[| "module HelloWorld"
""
"[<EntryPoint>]"
"let main _ ="
" // This code displays a simple greeting"
" // to the console."
" printfn \"Hello, World.\""
" 0" |]
printfn "Before call to StripComments:"
for line in lines do
printfn $" {line}"
let strippedLines = stripComments lines
printfn "After call to StripComments:"
for line in strippedLines do
printfn $" {line}"
// This code produces the following output to the console:
// Before call to StripComments:
// module HelloWorld
//
// [<EntryPoint>]
// let main _ =
// // This code displays a simple greeting
// // to the console.
// printfn "Hello, World."
// 0
// After call to StripComments:
// This code displays a simple greeting
// to the console.
Public Shared Sub Main()
Dim lines() As String = {"Public Module HelloWorld", _
" Public Sub Main()", _
" ' This code displays a simple greeting", _
" ' to the console.", _
" Console.WriteLine(""Hello, World."")", _
" End Sub", _
" End Module"}
Console.WriteLine("Code before call to StripComments:")
For Each line As String In lines
Console.WriteLine(" {0}", line)
Next
Dim strippedLines() As String = StripComments(lines)
Console.WriteLine("Code after call to StripComments:")
For Each line As String In strippedLines
Console.WriteLine(" {0}", line)
Next
End Sub
' This code produces the following output to the console:
' Code before call to StripComments:
' Public Module HelloWorld
' Public Sub Main()
' ' This code displays a simple greeting
' ' to the console.
' Console.WriteLine("Hello, World.")
' End Sub
' End Module
' Code after call to StripComments:
' This code displays a simple greeting
' to the console.
備註
方法 TrimStart(System.Char[])
會從目前字串中移除參數中的所有 trimChars
前置字元。 當遇到不在 中的 trimChars
字元時,修剪作業會停止。 例如,如果目前的字串為 「123abc456xyz789」,且 trimChars
包含 「1」 到 「9」 的數位,則 TrimStart(System.Char[])
方法會傳回 「abc456xyz789」。
注意
TrimStart(System.Char[])
如果方法從目前實例移除任何字元,這個方法就不會修改目前實例的值。 相反地,它會傳回新的字串,其中會移除目前實例中找到之參數中的所有 trimChars
前置字元。
給呼叫者的注意事項
.NET Framework 3.5 SP1 和舊版會維護此方法在 為 null
或空陣列時 trimChars
修剪的內部空白字元清單。 從 .NET Framework 4 開始,如果 為 trimChars
null
或空陣列,則方法會修剪所有 Unicode 空白字元 (,也就是將傳回值傳遞給 IsWhiteSpace(Char) 方法時產生 true
傳回值的字元) 。 由於這項變更, Trim() .NET Framework 3.5 SP1 和較舊版本中的 方法會移除兩個字元:零寬度空格 (U+200B) 和零寬度 NO-BREAK SPACE (U+FEFF) , Trim() .NET Framework 4 和更新版本中的方法不會移除。 此外, Trim() .NET Framework 3.5 SP1 和較舊版本中的 方法不會修剪三個 Unicode 空白字元:在 U+180E (U+180E) 、NARROW NO-BREAK SPACE (U+202F) ,以及中數學空間 (U+205F) 。
另請參閱
適用於
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