声明一个负长度的数组 [英] Declaring an array of negative length

问题描述

在 C 中创建负长度数组时会发生什么?

What happens in C when you create an array of negative length?

例如:

int n = -35;

int testArray[n];

for(int i = 0; i < 10; i++)
    testArray[i]=i+1;

此代码将编译(并且在启用 -Wall 时不会出现警告)，而且您似乎可以毫无问题地分配给 testArray[0].分配过去会导致段错误或非法指令错误，并从数组中读取任何内容都会说中止陷阱"(我不熟悉那个).我意识到这有点学术性，并且(希望)永远不会出现在现实生活中，但是 C 标准是否有任何特定的方式来处理此类数组，或者它是否因编译器而异?

This code will compile (and brings up no warnings with -Wall enabled), and it seems you can assign to testArray[0] without issue. Assigning past that gives either a segfault or illegal instruction error, and reading anything from the array says "Abort trap" (I'm not familiar with that one). I realize this is somewhat academic, and would (hopefully) never come up in real life, but is there any particular way that the C standard says to treat such arrays, or is does it vary from compiler to compiler?

推荐答案

这是未定义的行为，因为它打破了应该"约束:

It's undefined behaviour, because it breaks a "shall" constraint:

C99 §6.7.5.2:

如果大小是一个表达式不是整数常量表达式......每次对其进行评估时，它都应具有大于零的值.

If the size is an expression that is not an integer constant expression... ...each time it is evaluated it shall have a value greater than zero.

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