constant pointer in C

Question

Possible Duplicate:
What is the difference between char s[] and char *s in C?

There's a program:

#include<stdio.h>

int main()
{
    char str[20] = "Hello";
    char *const p=str;
    *p='M';
    printf("%s\n", str);
    return 0;
}

This prints Mello as the answer.. But since p is a constant pointer, shouldn't it give an error?

read difference between constant pointers and pointer to constants — Baz1nga, Sep 22 '12 at 13:32

score 15 · Accepted Answer · answered Sep 22 '12 at 13:32

15

It's a contant pointer, exactly. You can't change where it points. You can change what it points.

const char *p;  // a pointer to const char
char * const p; // a const pointer to char
const char * const p; //combined...

The easiest way to memorize the syntax is to not memorize it at all. Just read the declaration from right to left :-)

answered Sep 22 '12 at 13:32

emesx

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Perfect answer! :) Made it all clear! :) – Rebooting Sep 22 '12 at 13:39

score 2 · Answer 2 · edited May 23 '17 at 10:25

2

char *const p; is a constant pointer to a char. So modifying the value pointed by p is perfectly legal.

There's a detailed explanation: const char vs. char const vs const *char const

edited May 23 '17 at 10:25

Community

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answered Sep 22 '12 at 13:31

P.P

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@Mat, right you are, deleting my comment (even though somebody agreed with me :) – Jens Gustedt Sep 22 '12 at 13:38

score 0 · Answer 3 · answered Sep 22 '12 at 13:31

0

You can't change the value of p, but you can change the value of *p.

If you had written char const *p=str or const char *p=str, then you would not have been able to modify *p.

answered Sep 22 '12 at 13:31

John Bode

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score 0 · Answer 4 · answered Sep 22 '12 at 13:32

There is a difference between a constant pointer and pointer to constant data. Consider these four:

const char * p=str;  // p[0] is const
char const * p=str;  // same
char *const p=str;   // p is const. *p is not
char const *const p=str; // p is const, p[0] also

constant pointer in C

4 Answers4