CODEWITHSUNDEEP
c
Motiejus Jakštys
Motiejus Jakštys

Reputation: 2979

Passing pointer to C array to a function

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;
}

Upvotes: 5

Views: 272

Answers (4)

Daniel Kamil Kozar
Daniel Kamil Kozar

Reputation: 19266

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.

Upvotes: 0

Constantinius
Constantinius

Reputation: 35039

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;

Upvotes: 2

jofel
jofel

Reputation: 3405

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

Upvotes: 0

ckruse
ckruse

Reputation: 9740

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

Upvotes: 0

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