c - 一旦超出范围，C 是否会重用本地 block var 的内存？

Question

(我认为这个问题在技术上与 Can a local variable's memory be accessed outside its scope? 不同，因为它是 C 而不是 C++。)

我知道在 C 中你可以把一个局部变量放在一个 block 中，它的作用域将是那个 block :

#include <stdio.h>
int main() {
    {
        int x = 5;
        printf("x = '%d'\n", x);
    }
    // can't see x anymore
}

我的问题是，在函数结束之前使用该内存仍然安全吗？从设计/编码实践的角度来看，它是否是 WISE 是一个单独的问题，但它是未定义的行为还是我可以指望该内存保持不变？例如:

#include <stdio.h>
int main() {
    int *ptr;

    {
        int x = 5;
        printf("x = '%d'\n", x);

        // hold on to a ptr while we still know the address
        ptr = &x;
    }

    // can't see x anymore, but is this safe?
    printf("still have a ptr! '%d'\n", *ptr);
}

谢谢!

Answer 1

C99，6.2.4 p2 标准说:

If an object is referred to outside of its lifetime, the behavior is undefined. The value of a pointer becomes indeterminate when the object it points to reaches the end of its lifetime.