C#ulong上溢/下溢以某种方式允许 [英] C# ulong overflow / underflow somehow allowed

问题描述

我对 ulong 类型的行为有些困惑.我了解它是用于64位整数正数(最大值18,446,744,073,709,551,615).我刚开始使用它是因为我需要非常大的正数，但是对于潜在的负数，我不了解某些奇怪的行为.

I'm a little confused about the behavior of the ulong type. I understand it to be a 64-bit integer used for positive numbers (max value 18,446,744,073,709,551,615). I just started using it because I need really big positive numbers, but there's some strange behavior I don't understand around potential negative numbers.

ulong big = 1000000;    //Perfectly legal

ulong negative = -1;    //"Constant value "-1" cannot be converted to a ulong" Makes sense


//Attempt to sneak around the -1 as a constant compile-time error
int negativeInt = -1;
ulong negativeUlongFail = negativeInt;    //"Cannot implicitly convert 'int' to 'ulong'.
                                 //An explicit conversion exists (are you missing a cast?)"
//So I add casting
ulong negativeUlong = (ulong)negativeInt;    //But this yields 18446744073709551615

//Try and get a negative number indirectly
ulong number = 0;
number = number - 10;  //now number is 18446744073709551615 but no underflow error

这是怎么回事?如何捕获一些下溢错误，而没有捕获甚至不抛出异常?我可以检测到这些吗?

我专注于通过下溢获得负数，但是当数字大于最大值并发生溢出时，我也看到过类似的事情.

I focused on getting negative numbers by underflowing, but I've seen similar things when getting numbers bigger than the max value and overflowing.

我不确定它们在技术上是错误还是例外，因此如果我使用了错误的术语，请原谅我

推荐答案

如果要引发下溢(或上溢)异常，请尝试以下方法:-

if you want the underflow (or overflow) exception to be thrown, try this instead :-

checked
{
    ulong number = 0;
    number = number - 10;
}

默认情况下，该异常会被吞下(运行时未经检查).

by default the exception gets swallowed (it runs in unchecked).

请参阅官方文档

https://docs.microsoft.com/en-us/dotnet/csharp/language-reference/keywords/checked

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