# unchecked（C# 参考）unchecked (C# Reference)

unchecked 关键字用于取消整型类型的算术运算和转换的溢出检查。The unchecked keyword is used to suppress overflow-checking for integral-type arithmetic operations and conversions.

unchecked
{
int1 = 2147483647 + 10;
}
int1 = unchecked(ConstantMax + 10);


## 示例Example

class UncheckedDemo
{
static void Main(string[] args)
{
// int.MaxValue is 2,147,483,647.
const int ConstantMax = int.MaxValue;
int int1;
int int2;
int variableMax = 2147483647;

// The following statements are checked by default at compile time. They do not
// compile.
//int1 = 2147483647 + 10;
//int1 = ConstantMax + 10;

// To enable the assignments to int1 to compile and run, place them inside
// an unchecked block or expression. The following statements compile and
// run.
unchecked
{
int1 = 2147483647 + 10;
}
int1 = unchecked(ConstantMax + 10);

// The sum of 2,147,483,647 and 10 is displayed as -2,147,483,639.
Console.WriteLine(int1);

// The following statement is unchecked by default at compile time and run
// time because the expression contains the variable variableMax. It causes
// overflow but the overflow is not detected. The statement compiles and runs.
int2 = variableMax + 10;

// Again, the sum of 2,147,483,647 and 10 is displayed as -2,147,483,639.
Console.WriteLine(int2);

// To catch the overflow in the assignment to int2 at run time, put the
// declaration in a checked block or expression. The following
// statements compile but raise an overflow exception at run time.
checked
{
//int2 = variableMax + 10;
}
//int2 = checked(variableMax + 10);

// Unchecked sections frequently are used to break out of a checked
// environment in order to improve performance in a portion of code
// that is not expected to raise overflow exceptions.
checked
{
// Code that might cause overflow should be executed in a checked
// environment.
unchecked
{
// This section is appropriate for code that you are confident
// will not result in overflow, and for which performance is
// a priority.
}
// Additional checked code here.
}
}
}