C++ – Are const char* and char const* the Same?

c++constantspointers

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

const char*

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

char const*

is a constant pointer to mutable chars.

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

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

Best Answer

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;

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

char * const constantPointerToMutableContent;

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

char const * const constantPointerToConstantContent;

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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