Passing pointer to C array to a function

Question

What do I misunderstand about passing pointers to char arrays?

Request pointer in fun: 0x7fffde9aec80
Response pointer in fun: 0x7fffde9aec80
Response pointer: (nil), expected: 0x7fffde9aec80
Response itself: (null), expected: Yadda

#include <stdlib.h>
#include <stdio.h>
#include <string.h>

int get_response(char *request, char **response) {
    response = &request;
    printf("Request pointer in fun: %p\n", request);
    printf("Response pointer in fun: %p\n", *response);
    return 0;
}

int main() {
    char *response = NULL, request[] = "Yadda";

    get_response(request, &response);

    printf("Response pointer: %p, expected: %p\n", response, request);
    printf("Response itself: %s, expected: %s\n", response, request);

    return 0;
}

@OliCharlesworth: He doesn't get why what gets printed does not match what he 'expects' to be printed: Response pointer: (nil), expected: 0x7fffde9aec80 Response itself: (null), expected: Yadda — ArjunShankar
– ArjunShankar, Commented Feb 23, 2012 at 14:18

Constantinius · Accepted Answer · 2012-02-23 14:12:59Z

2

in the function get_response you store the address of request in the temporary variable response. You want to store it where response points to.

*response = request;

answered Feb 23, 2012 at 14:12

Constantinius

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1 Comment

ArjunShankar Over a year ago

+1 for explaining what OP is 'misunderstanding'. i.e. changing an argument's value instead of changing the location which the argument points to.

ckruse · Accepted Answer · 2012-02-23 14:12:22Z

0

Try *response = request: you want to set the contents of the response pointer to the request content.

answered Feb 23, 2012 at 14:12

ckruse

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Comments

jofel · Accepted Answer · 2012-02-23 14:12:41Z

0

You want *response = request; instead of response = &request; in get_response(...)

answered Feb 23, 2012 at 14:12

jofel

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Comments

Daniel Kamil Kozar · Accepted Answer · 2012-02-23 14:13:09Z

0

Firstly, with the currect declaration and your usage of get_response, the parameter response is declared as char**, which is a pointer to a char*, e.g. a pointer to a pointer. This would be useful if you somehow needed to modify the pointer actually pointing to the memory containing your response, but in this case this is not needed.

answered Feb 23, 2012 at 14:13

Daniel Kamil Kozar

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