checked（C# 参考） · MSDN C# 编程指南 & 参考手册 2015

# checked（C# 参考） **checked** 关键字用于对整型算术运算和转换显式启用溢出检查。默认情况下，如果表达式仅包含常数值，且产生的值在目标类型范围之外，则它会导致编译器错误。如果表达式包含一个或多个非常数值，则编译器不检测溢出。在下面的示例中，计算赋给 i2 的表达式不会导致编译器错误。 ``` // The following example causes compiler error CS0220 because 2147483647 // is the maximum value for integers. //int i1 = 2147483647 + 10; // The following example, which includes variable ten, does not cause // a compiler error. int ten = 10; int i2 = 2147483647 + ten; // By default, the overflow in the previous statement also does // not cause a run-time exception. The following line displays // -2,147,483,639 as the sum of 2,147,483,647 and 10. Console.WriteLine(i2); ``` 默认情况下，在运行时也不检查这些非常数表达式是否溢出，这些表达式不引发溢出异常。上面的示例显示 -2,147,483,639 作为两个正整数之和。可以通过编译器选项、环境配置或使用 **checked** 关键字来启用溢出检查。下面的示例演示如何使用 **checked** 表达式或 **checked** 块，在运行时检测由前面的求和计算导致的溢出。两个示例都引发溢出异常。 ``` // If the previous sum is attempted in a checked environment, an // OverflowException error is raised. // Checked expression. Console.WriteLine(checked(2147483647 + ten)); // Checked block. checked { int i3 = 2147483647 + ten; Console.WriteLine(i3); } ``` 可以使用 [unchecked](https://msdn.microsoft.com/zh-cn/library/a569z7k8.aspx) 关键字阻止溢出检查。此示例演示如何使用 **checked** 启用运行时溢出检查。 ``` class OverFlowTest { // Set maxIntValue to the maximum value for integers. static int maxIntValue = 2147483647; // Using a checked expression. static int CheckedMethod() { int z = 0; try { // The following line raises an exception because it is checked. z = checked(maxIntValue + 10); } catch (System.OverflowException e) { // The following line displays information about the error. Console.WriteLine("CHECKED and CAUGHT: " + e.ToString()); } // The value of z is still 0. return z; } // Using an unchecked expression. static int UncheckedMethod() { int z = 0; try { // The following calculation is unchecked and will not // raise an exception. z = maxIntValue + 10; } catch (System.OverflowException e) { // The following line will not be executed. Console.WriteLine("UNCHECKED and CAUGHT: " + e.ToString()); } // Because of the undetected overflow, the sum of 2147483647 + 10 is // returned as -2147483639. return z; } static void Main() { Console.WriteLine("\nCHECKED output value is: {0}", CheckedMethod()); Console.WriteLine("UNCHECKED output value is: {0}", UncheckedMethod()); } /* Output: CHECKED and CAUGHT: System.OverflowException: Arithmetic operation resulted in an overflow. at ConsoleApplication1.OverFlowTest.CheckedMethod() CHECKED output value is: 0 UNCHECKED output value is: -2147483639 */ } ``` ## C# 语言规范有关详细信息，请参阅 [C# 语言规范](https://msdn.microsoft.com/zh-cn/library/ms228593.aspx)。该语言规范是 C# 语法和用法的权威资料。 ## 请参阅 [C# 参考](https://msdn.microsoft.com/zh-cn/library/618ayhy6.aspx) [C# 编程指南](https://msdn.microsoft.com/zh-cn/library/67ef8sbd.aspx) [C# 关键字](https://msdn.microsoft.com/zh-cn/library/x53a06bb.aspx) [Checked 和 Unchecked（C# 参考）](https://msdn.microsoft.com/zh-cn/library/khy08726.aspx) [unchecked（C# 参考）](https://msdn.microsoft.com/zh-cn/library/a569z7k8.aspx)