const char *和char const * - 它们是否相同？ [英] const char* and char const* - are they the same?

问题描述

从我的理解， const 修饰符应该从右到左读。从中我得到：

From my understanding, const modifiers should be read from right to left. From that, I get that:

const char*

是一个指针，其char元素不能修改，但指针本身可以修改，

is a pointer whose char elements can't be modified, but the pointer itself can, and

char const*

是一个常量指针，指向 mutable

is a constant pointer to mutable chars.

但我收到以下代码的以下错误：

But I get the following errors for the following code:

const char* x = new char[20];
x = new char[30];   //this works, as expected
x[0] = 'a';         //gives an error as expected

char const* y = new char[20];
y = new char[20];   //this works, although the pointer should be const (right?)
y[0] = 'a';         //this doesn't although I expect it to work

那么是哪一个呢？我的理解或我的编译器（VS 2005）错了？

So... which one is it? Is my understanding or my compiler(VS 2005) wrong?

推荐答案

实际上，根据标准， const 将元素直接修改为其左边。在声明开始使用 const 只是一个方便的心理快捷方式。因此，以下两个语句是等效的：

Actually, according to the standard, const modifies the element directly to its left. The use of const at the beginning of a declaration is just a convenient mental shortcut. So the following two statements are equivalent:

char const * pointerToConstantContent1;
const char * pointerToConstantContent2;

为了确保指针本身不被修改， const 应放在星号后面：

In order to ensure the pointer itself is not modified, const should be placed after the asterisk:

char * const constantPointerToMutableContent;

要保护指针及其指向的内容，请使用两个常数。

To protect both the pointer and the content to which it points, use two consts.

char const * const constantPointerToConstantContent;

我已经亲自采用了不修改，即使指针是我希望保持不变的部分，我仍保持一致。

I've personally adopted always putting the const after the portion I intend not to modify such that I maintain consistency even when the pointer is the part I wish to keep constant.

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