c - 为什么静态数组工作

Question

我是 C 程序员并且正在使用

gcc (Ubuntu/Linaro 4.7.3-1ubuntu1) 4.7.3

下面的静态数组正在工作

int i=10;

int a[i];

---

它工作正常，但根据我的说法，它应该在这种类型的数组声明中给出错误， 任何人都可以告诉我这是什么行为？

Answer 1

你是对的 - 根据 C99 standard , section 6.7.5.2, part 2, static arrays cannot be declared with variable length:

Only an ordinary identifier (as defined in 6.2.3) with both block scope or function prototype scope and no linkage shall have a variably modified type. If an identifier is declared to be an object with static storage duration, it shall not have a variable length array type. (emphasis added)

#include <stdio.h>
int i = 5;
int a[i]; // <<== ERROR - this does not compile

( demo showing this error )

对于非静态数组(例如自动存储区中的数组，也称为“栈”)，这是允许的。此外，您甚至可以从函数外部传递 i:

void test(int i) {
    int a[i]; // C99 allows this; gcc allows this in c90 as well.
}

gcc allows variable length arrays in C90 as an extension .