Realloc struct array as a function parameter yields segmentation fault? - c

Question

I have searched quite a bit, before asking, but I can't seem to make this function work.
I have this array of structs with 2 strings (char*)
and the function put() that adds a new struct, Unless the key already exists in that case it just ovewrites the current value with the new one.
Despite I am passing the array by reference and not making a local copy in the function, the memory still is corrupted (Segmentation Fault).
The source code is compiled under Ubuntu 15.10 on latest version of gcc.
Thanks in advance for your help guys!
#include <stdio.h>
#include <string.h>
#include <stdlib.h>
#define N 3
struct store{
char *key;
char *value;
};
void put(char *key, char *value, struct store **store, int size){
int i, found;
struct store *temp = realloc(*store, (size + 1) * sizeof(struct store));
for(i = 0; i < size; ++i){
if(strcmp(key, store[i]->key) == 0){ //Key found, overwrite new value.
store[i]->value = strdup(value); //Assume that every value is null terminated
found = 1;
break;
}
}
if(found) return;
*store = temp;
if(!store){
perror("realloc failed");
exit(EXIT_FAILURE);
}
store[size]->key = strdup(key); //New element
store[size]->value = strdup(value);
return;
}
int main(){
int i = 0;
struct store *store = malloc(N * sizeof(struct store));
if(!store){
perror("malloc failed");
exit(EXIT_FAILURE);
}
store[0].key = strdup("123a");
store[1].key = strdup("456b");
store[2].key = strdup("789c");
store[0].value = strdup("John");
store[1].value = strdup("Sam");
store[2].value = strdup("Mary");
for(i = 0; i < N; ++i)
printf("%s, %s\n\n",store[i].key,store[i].value); //This works fine
put("123a","Jim",&store,N);
for(i = 0; i < N; ++i)
printf("%s, %s\n\n",store[i].key,store[i].value);
put("653a","Tom",&store,N);
for(i = 0; i < N+1; ++i)
printf("%s, %s\n\n",store[i].key,store[i].value);
return 0;
}

Answer 1

struct store *temp = realloc(*store, (size + 1) * sizeof(struct store));
for(i = 0; i < size; ++i){
if(strcmp(key, store[i]->key) == 0){ //Key found, overwrite new value.
store[i]->value = strdup(value); //Assume that every value is null terminated
found = 1;
break;
}
}
if(found) return;
*store = temp;
If the key is found, you don't assign temp to *store. realloc can move the allocated memory to a completely new address, thus leaving *store a dangling pointer. And you really should also check that temp isn't null as well.
There's also the problem of your misuse of store. store is the the address of the pointer you passed into the function, not the first element of an array.
You need to index the array like this (*store)[i].