为什么全局变量总是初始化为“0"，而不是局部变量? [英] Why are global variables always initialized to '0', but not local variables?

问题描述

可能的重复:
为什么将全局和静态变量初始化为默认值值?

查看代码，

#include <stdio.h>

int a;
int main(void)
{
    int i;
    printf("%d %d
", a, i);
}

输出

0 8683508

这里的a"用0"初始化，但i"用垃圾值"初始化.为什么?

Here 'a' is initialized with '0', but 'i' is initialized with a 'junk value'. Why?

推荐答案

因为根据 C 标准，事情就是这样.这样做的原因是效率:

Because that's the way it is, according to the C Standard. The reason for that is efficiency:

• static 变量在编译时初始化，因为它们的地址是已知和固定的.将它们初始化为 0 不会产生运行时成本.

• static variables are initialized at compile-time, since their address is known and fixed. Initializing them to 0 does not incur a runtime cost.

自动变量对于不同的调用可以有不同的地址，并且必须在每次调用函数时在运行时初始化，从而产生运行成本不需要.如果您确实需要初始化，请请求它.

automatic variables can have different addresses for different calls and would have to be initialized at runtime each time the function is called, incurring a runtime cost that may not be needed. If you do need that initialization, then request it.

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