声明负长度的数组 [英] Declaring an array of negative length

问题描述

在C当您创建负长度的数组，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;

这code编译（并带来了-Wall没有警告启用），似乎可以分配给 testArray [0] 没有问题。过去的分配，让无论是段错误或非法指令错误，阅读任何东西从阵列中说，中止陷阱（我不熟悉的那一个）。我知道这是有点学术，并会（希望）从来没有拿出在现实生活中，但有，在C标准说来治疗这类阵列任何特殊的方式，或者是它与编译器有所不同编译器？

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

这是不确定的行为，因为它打破了应当的约束：

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

C99§6.7.5.2：

如果大小是前pression即
  不是一个整数常量前pression ...
  ......每次被评价应
  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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