C# 变量和常量在溢出期间的行为不同。

Question

 const int cMax = int.MaxValue;
 int vMax = cMax;
 int int1;
 int int2;
 int1 = cMax + 10;//Checked amd throws error
 int2 = vMax+10;//Unchecked and Overflows at runTime

这里可以看到涉及常量的操作默认是被检查的，而涉及变量的操作是未检查的并且通过了编译。

为什么编译行为会出现这种差异？

Answer 1

行为不同，因为 cMax + 10 是常量表达式。根据C# Language Reference ,

A constant expression is an expression that can be fully evaluated at compile time. A constant can participate in a constant expression, as follows:

public const int c1 = 5;  
public const int c2 = c1 + 100;

By default, an expression that contains only constant values causes a compiler error if the expression produces a value that is outside the range of the destination type. If the expression contains one or more non-constant values, the compiler does not detect the overflow.

因此，编译器必须在编译时评估您的表达式。由于它无法生成有效值作为计算结果，因此会产生编译时错误。使用 checked keyword启用整数溢出检查。