printf 打印不稳定 [英] Erratic printing by printf

问题描述

以下代码片段虽然完全相同但给出了不同的答案

The following code snippets although quite same but giving different answers

#include <stdio.h>
int main() {
  signed char c = -128;
  c = -c;
  printf("%d", c);.  //-128
  return 0;
}

还有:

#include <stdio.h>
int main() {
  signed char c = -128;
  printf("%d", -c);.  //expected -128 but got 128
  return 0;
}

printf 可以进行内部类型转换吗??

Could printf be doing internal typecasting??

推荐答案

签名类型的欠/溢出是未定义的行为，你不应该依赖它.

Under/Overflow of signed types is undefined behavior, you should not rely on it.

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