Get value of structure inside a structure array - c

Question

typedef struct{
int number;
char name[100];
} Apple
typedef struct{
Apple *apple;
int bit[2];
} AppleArray;
int main(){
AppleArray *aArray;
loadApple(&aArray);
}
loadApple(AppleArray **aArray){
*aArray = NULL;
for(i=0; i<100; i++){
*aArray = realloc(*aArray, (i+1) * sizeof(AppleArray));
/*SEGFAULT here*/
aArray[i]->apple = NULL;
for(j=0; j<2; j++){
aArray[i]->apple = realloc(aArray[i]->apple, sizeof(Apple) * (j+1))
}
}
}
I want to have an AppleArray with specific size. Each AppleArray will have two Apple. However, I get segfault when i assign NULL to aArray[i]->apple. What is the problem there?
EDIT :
loadApple(AppleArray **aArray){
*aArray = malloc(100 * sizeof(AppleArray));
for(i=0; i<100; i++){
/*SEGFAULT here*/
aArray[i]->apple = NULL;
for(j=0; j<2; j++){
aArray[i]->apple = realloc(aArray[i]->apple, sizeof(Apple) * (j+1))
}
}
}

Answer 1

You can call realloc() only on an address that was returned to you by an prior memory allocation function like malloc()or calloc() otherwise it gives you Undefined Behavior.
C99 Standard 7.20.3.4-3: The realloc function:
void *realloc(void *ptr, size_t size);
If ptr is a null pointer, the realloc function behaves like the malloc function for the
specified size. Otherwise, if ptr does not match a pointer earlier returned by a memory
management function, or if the space has been deallocated by a call to the free or
realloc function, the behavior is undefined.

Answer 2

Apart from what Als has mentioned above, you are also having an array out-of-bounds read problem as after your loop, i value will be 100 and you are trying to access aArray[100] whereas in your logic (though incorrect) your would have allocated memory only till aArray[99].
Your loadApple function can be rewritten as below:
loadApple(AppleArray **aArray)
{
*aArray = NULL;
*aArray = malloc(100 * sizeof(AppleArray));
//I have shown index as 0 here just as an example.
(*aArray)[0].apple = NULL;
(*aArray)[0].apple = malloc(2 * sizeof(Apple));
}
This code should also give the same behavior which the logic of your code is trying to achieve.

Answer 3

<pre>
#include "stdio.h"
#include "stdlib.h"
#define MAX_SIZE 5
#define NAME_SIZE 100
#define APPLE_NUM 2
typedef struct
{
int number;
char name[NAME_SIZE];
}Apple;
typedef struct
{
Apple* apple;
int bit[2];
}AppleArray;
void printApple(AppleArray** aArray)
{
int i;
for (i = 0; i < MAX_SIZE; ++i)
{
fprintf(stderr, "%4d: bit[0] = %d, bit[1] = %d\n", i, (*aArray + i)->bit[0], (*aArray + i)->bit[1]);
int j;
for (j = 0; j < APPLE_NUM; ++j)
{
fprintf(stderr, "\tapple[%d]: number = %d, name = %s\n",
j,
(*aArray + i)->apple[j].number,
(*aArray + i)->apple[j].name);
}
printf("\n");
}
}
void loadApple(AppleArray **aArray)
{
*aArray = NULL;
int i;
for(i = 0; i < MAX_SIZE; i++)
{
AppleArray* tmp = (AppleArray*)realloc(*aArray, (i+1) * sizeof(AppleArray));
if (tmp != NULL)
{
*aArray = tmp;
}
else
{
//error
free(*aArray);
*aArray = NULL;
exit(0);
}
/*SEGFAULT here*/
//aArray[i]->apple = NULL;
(*aArray + i)->apple = NULL;
(*aArray + i)->bit[0] = i;
(*aArray + i)->bit[1] = i + 1;
/*
int j;
for (j = 0; j < 2; j++)
{
(*aArray + i)->apple = realloc(aArray[i]->apple, sizeof(Apple) * (j+1));
}
*/
(*aArray + i)->apple = (Apple*)realloc(NULL, sizeof(Apple) * APPLE_NUM);
int j;
for (j = 0; j < APPLE_NUM; ++j)
{
(*aArray + i)->apple[j].number = j;
snprintf( (*aArray + i)->apple[j].name, NAME_SIZE, "apple_%d_%d", i, j);
}
}//for
}
void destroyApple(AppleArray* thiz)
{
if (thiz == NULL)
{
return;
}
int i;
for (i = 0; i < MAX_SIZE; ++i)
{
free(thiz[i].apple);
thiz[i].apple = NULL;
}
free(thiz);
}
int main()
{
AppleArray *aArray;
loadApple(&aArray);
printApple(&aArray);
destroyApple(aArray);
return 0;
}