为什么我可以改变一个const char *变量的值？ [英] Why can I change the value of a const char* variable?

问题描述

为什么以下code用C的工作？

Why does the following code in C work?

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

由于str是一个指向一个恒定的性格，为什么我们允许它分配不同的字符串？此外，我们如何保护海峡被修改？这似乎是如果，例如，我们以后被分配海峡到最后写了内存另一部分更长的字符串，这可能是一个问题。

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.

我要补充一点，在我的测试中，我打印出str的内存地址之前和之后我的每个任务的，它从来没有改变过。因此，虽然str是一个指针，指向一个const char，内存实际上是被修改。我想，如果这也许是一个遗留问题，用C？

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

您正在改变的指针，这是不是常量（某事物的指向是常量）。

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

如果你想指针本身是常量，声明将如下所示：

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

常量指向非const数据通常比指针到常量。不太有用的结构

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

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