c - Problem with calling realloc inside function where an array is a parameter

Question

This question already has an answer here: question from:https://stackoverflow.com/questions/65599191/problem-with-calling-realloc-inside-function-where-an-array-is-a-parameter

Answer 1

The argument tab of the function sth is a copy of what is passed and change to that won't affect what is passed. Therefore, free(tab); in the main() function means free(NULL);. This is defined to do nothing and it won't contribute for avoiding memory leak. Pass pointers to what should be modified to have functions modify what are passed.

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

struct x{
    int a;
    char b;
};


void allocate( struct x **tab,int *size)
{
    *size = 1+2*(*size);
    *tab= realloc(*tab, (size_t) (*size) * sizeof (**tab));
}


void sth (struct x **tab, int *size) // receive a pointer of struct x*
{
    //do something here
    // allocate(&(*tab), size);
    allocate(tab, size);
}

int main(void)
{
    int size=0;
    struct x *tab=NULL;
    sth(&tab, &size); // pass a pointer to what should be modified
    //do sth here with tab
    free(tab);
    return 0;
}