为什么我可以更改 const char* 变量的值? [英] Why can I change the value of a const char* variable?

问题描述

为什么下面的 C 代码可以工作?

Why does the following code in C work?

const char* str = NULL;
str = "test";
str = "test2";

既然 str 是一个指向常量字符的指针，为什么我们可以给它分配不同的字符串字面量呢?此外，我们如何保护 str 不被修改?例如，如果我们稍后将 str 分配给一个更长的字符串，该字符串最终会覆盖另一部分内存，这似乎是一个问题.

Since str is a pointer to a constant character, why are we allowed to assign it different string literals? Further, how can we protect str from being modified? It seems like this could be a problem if, for example, we later assigned str to a longer string which ended up writing over another portion of memory.

我应该在我的测试中补充一点，我在每次分配之前和之后打印出 str 的内存地址，它从未改变过.因此，尽管 str 是一个指向 const char 的指针，但实际上内存正在被修改.我想知道这是否是 C 的遗留问题?

I should add that in my test, I printed out the memory address of str before and after each of my assignments and it never changed. So, although str is a pointer to a const char, the memory is actually being modified. I wondered if perhaps this is a legacy issue with C?

推荐答案

你正在改变指针，它不是 const(它指向的东西是 const).

You are changing the pointer, which is not const (the thing it's pointing to is const).

如果您希望指针本身为 const，则声明如下:

If you want the pointer itself to be const, the declaration would look like:

char * const str = "something";

或

char const * const str = "something";  // a const pointer to const char
const char * const str = "something";  //    same thing

指向非 const 数据的 const 指针通常不如指向 const 的指针有用.

Const pointers to non-const data are usually a less useful construct than pointer-to-const.

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