What is the difference between char * const and co

Question

What's the difference between:

char * const 

and

const char *

Answer 1

I presume you mean const char * and char * const .

The first, const char *, is a pointer to a constant character. The pointer itself is mutable.

The second, char * const is a constant pointer to a character. The pointer cannot change, the character it points to can.

And then there is const char * const where the pointer and character cannot change.

Answer 2

char * const and const char *?

1. Pointing to a constant value

const char * p; // value cannot be changed

2. Constant pointer to a value

char * const p; // address cannot be changed

3. Constant pointer to a constant value

const char * const p; // both cannot be changed.

Answer 3

Here is a detailed explanation with code

/*const char * p;
char * const p; 
const char * const p;*/ // these are the three conditions,

// const char *p;const char * const p; pointer value cannot be changed

// char * const p; pointer address cannot be changed

// const char * const p; both cannot be changed.

#include<stdio.h>

/*int main()
{
    const char * p; // value cannot be changed
    char z;
    //*p = 'c'; // this will not work
    p = &z;
    printf(" %c\n",*p);
    return 0;
}*/

/*int main()
{
    char * const p; // address cannot be changed
    char z;
    *p = 'c'; 
    //p = &z;   // this will not work
    printf(" %c\n",*p);
    return 0;
}*/



/*int main()
{
    const char * const p; // both address and value cannot be changed
    char z;
    *p = 'c'; // this will not work
    p = &z; // this will not work
    printf(" %c\n",*p);
    return 0;
}*/

Answer 4

First one is a syntax error. Maybe you meant the difference between

const char * mychar

and

char * const mychar

In that case, the first one is a pointer to data that can't change, and the second one is a pointer that will always point to the same address.

Answer 5

The difference is that const char * is a pointer to a const char, while char * const is a constant pointer to a char.

The first, the value being pointed to can't be changed but the pointer can be. The second, the value being pointed at can change but the pointer can't (similar to a reference).

There is also a

const char * const

which is a constant pointer to a constant char (so nothing about it can be changed).

Note:

The following two forms are equivalent:

const char *

and

char const *

The exact reason for this is described in the C++ standard, but it's important to note and avoid the confusion. I know several coding standards that prefer:

char const

over

const char

(with or without pointer) so that the placement of the const element is the same as with a pointer const.

Answer 6

Rule of thumb: read the definition from right to left!

---

const int *foo;

Means "foo points (*) to an int that cannot change (const)".
To the programmer this means "I will not change the value of what foo points to".

• *foo = 123; or foo[0] = 123; would be invalid.
• foo = &bar; is allowed.

---

int *const foo;

Means "foo cannot change (const) and points (*) to an int".
To the programmer this means "I will not change the memory address that foo refers to".

• *foo = 123; or foo[0] = 123; is allowed.
• foo = &bar; would be invalid.

---

const int *const foo;

Means "foo cannot change (const) and points (*) to an int that cannot change (const)".
To the programmer this means "I will not change the value of what foo points to, nor will I change the address that foo refers to".

• *foo = 123; or foo[0] = 123; would be invalid.
• foo = &bar; would be invalid.