如果我为一个无符号变量赋值一个负值会发生什么？ [英] What happens if I assign a negative value to an unsigned variable?

问题描述

我想知道如果我给一个无符号变量赋一个负值会发生什么。

  unsigned int nVal = 0; 
 nVal = -5; 
  

它没有给我任何编译器错误。当我运行程序时， nVal 被分配了一个奇怪的值！是否可以将一些2的补码值分配给 nVal ？

解决方案

正式答案 - 第4.7节[conv.integral]

如果目标类型是无符号，结果值是最小无符号整数等于源整数（模2 ^ n，其中n是用于表示无符号类型的位数）[注：在二进制补码表示中，此转换是概念性的，并且位模式没有变化没有截断）。-end note]

I was curious to know what would happen if I assign a negative value to an unsigned variable.

The code will look somewhat like this.

unsigned int nVal = 0;
nVal = -5;

It didn't give me any compiler error. When I ran the program the nVal was assigned a strange value! Could it be that some 2's complement value gets assigned to nVal?

解决方案

For the official answer - Section 4.7 [conv.integral]

"If the destination type is unsigned, the resulting value is the least unsigned integer congruent to the source integer (modulo 2^n where n is the number of bits used to represent the unsigned type). [ Note: In a two’s complement representation, this conversion is conceptual and there is no change in the bit pattern (if there is no truncation). —end note ]

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