c - 修改常量变量(const)

Question

这个问题已经有答案了:

Why are we allowed to change values of "const" qualified variables?Why pointers are allowed for this,but not assignment? (2 个回答)

已关闭 7 年前。

我遇到了这段代码，我可以在其中修改 const int 的值多变的!但这是错误还是黑客行为？请澄清我:

#include<stdio.h>
int main(void)
{
    const int a = 10;
    int* ptr = &a;

    printf("\n value at ptr is  : [%d]\n",*ptr);
    printf("\n Address pointed by ptr  : [%p]\n",(unsigned int*)ptr);

    *ptr = 11;
    printf("\n value at ptr is  : [%d]\n",*ptr);
    printf("\n %d",a);

    return 0;
}

输出:

value at ptr is : [10]

Address pointed by ptr : [0xbf9e614c]

value at ptr is : [11]

11

Answer 1

不，这是undefined behaviour .

如果您尝试通过非常量限定符指针修改 const 限定变量，它将调用 UB。

引用 C11，第 §6.7.3 章，类型限定符

If an attempt is made to modify an object defined with a const-qualified type through use of an lvalue with non-const-qualified type, the behavior is undefined.