Dynamic memory allocation gives error while accessing

Question

I have a problem with my code:

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

void a(void *po, size_t t)
{
    void *r = realloc(po, t);
}


int main()
{
    uint8_t *array = NULL;

    a(array, sizeof(uint8_t) * 2);

    array[0] = 1;
    array[1] = 3;

    return 0;
}

When trying to insert data into the array this error appears:

 segmentation fault

Answer 1

The first problem is that you are relocating the object and playing on the variable r who dies there. It seems he wants to play in po even to reflect on array in the calling function.

But then we find another problem, you don’t want to pass the object but the pointer to the object, so you must pass &array to grab a pointer to array, which happens to be a pointer. And of course, the parameter should receive a pointer to what it will receive, so it should be a pointer to another pointer. And the right guy over there is uint8_t.

Fixing these problems you pass a memory address to a function, it will be changed to another address and as it went by reference it is changed in the variable that served as argument, which is what you want.

I hope this is just to demonstrate the mechanism because in real code it doesn’t make much sense to do this.

The way it was nothing was changed into array that kept pointing to null.

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

void a(uint8_t **po, size_t t) {
    *po = realloc(*po, t);
}

int main() {
    uint8_t *array = NULL;
    a(&array, sizeof(uint8_t) * 2);
    array[0] = 1;
    array[1] = 3;
}

Behold working in the ideone. And in the repl it.. Also put on the Github for future reference.