c++ 尝试反向打印数组时出现分段错误

2022-01-12 00:00:00 arrays segmentation-fault c++

我有一个由 [1,2,3,4,5,.,..] 之类的字符组成的数组，并且我有一个看起来像

I have a array consisting of chars like [1,2,3,4,5,.,..] and I have a loop that looks like 

  for (size_t i = 0; i < size; ++i)
    os << data[i]; // os is std::ostream&

此循环以正确的顺序打印数组，没有任何错误.但是当我使用这个循环向后打印时

This loop prints the array in the correct order without any errors. But when I use this loop to print it backwards

  for (size_t i = (size - 1); i >= 0; --i)
    os << data[i];

我收到分段错误错误.为什么会发生这种情况?

I get a segmentation fault error. Any reason why this can happen?

推荐答案

条件 i >= 0 始终为真(因为 size_t 是无符号类型).你写了一个无限循环.

The condition i >= 0 is always true (because size_t is an unsigned type). You've written an infinite loop.

你的编译器不会警告你吗?我知道 g++ -Wextra 在这里.

Doesn't your compiler warn you about that? I know g++ -Wextra does here.

您可以这样做:

for (size_t i = size; i--; ) {
    os << data[i];
}

这使用后减量来检查 i 的旧值，这允许循环在 i = 0 之后停止(此时 >i 已环绕到 SIZE_MAX).

This uses post-decrement to be able to check the old value of i, which allows the loop to stop just after i = 0 (at which point i has wrapped around to SIZE_MAX).

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