free function seems to not work

Question

I have this problem in C, happened about 3 times and I just cant find the answer. I'm allocating a memory in a create function, and when I'm trying to free it in a destroy the program crashes.

Here is the program:

typedef struct Order_t* Order;
struct Order_t {
    char* email;
    TechnionFaculty faculty;
    int id;
    char* time;
    int num_ppl;
};

Order createOrder(char* email, TechnionFaculty faculty, int id, char* time,
    int num_ppl)
{
    if (email == NULL) {
        return NULL;
    }
    if (checkEmail(email) != OK)
        return NULL;
    if (checkFaculty(faculty) != OK)
        return NULL;
    Order order = malloc(sizeof(Order));
    if (order == NULL)
        return NULL;
    (order->email) = malloc(strlen(email) + 1);
    if (order->email == NULL) {
        free(order);
        return NULL;
    }
    strcpy(order->email, email);
    order->faculty = faculty;
    order->id = id;
    order->num_ppl = num_ppl;
    order->time = malloc(strlen(time) + 1);
    if (order->time == NULL) {
        free(order->email);
        free(order);
        return NULL;
    }
    return order;
}

void orderDestroy(Order order)
{
    assert(order != NULL);
    free(order->email);
    free(order->time);
    free(order);
}

Answer 1

I did some small changes to your code so that it doesn't crash. When using a struct you should allocate both the struct and its members. I hope it can help you.

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

typedef struct Order_t *Order;
struct Order_t{
    char* email;
    //TechnionFaculty faculty;
    int id;
    char* time;
    int num_ppl;
};

Order createOrder (char* email, int id, char* time, int num_ppl){
    if (email == NULL) {
        return NULL;
    }

    Order order = malloc(sizeof(struct Order_t));
    if (order == NULL)
        return NULL;
    (order->email) = malloc(strlen(email)+1);
    if (order->email == NULL){
        free(order);
        return NULL;
    }
    strcpy(order->email, email);
    order->id = id;
    order->num_ppl = num_ppl;
    (order->time) = malloc(strlen(time)+1);
    if (order->time == NULL){
        free(order->email);
        free(order);
        return NULL;
    }
    return order;
}

void orderDestroy (Order order){
    assert(order != NULL);
    free(order->email);
    free(order->time);
    free(order);
}

int main() {
    printf("Hello, World!\n");
    Order o1 = createOrder("foo", 42, "24", 420);
    orderDestroy(o1);
    return 0;
}

We check it with valgrind.

$ ./a.out 
Hello, World!
developer@1604:~/CLionProjects/untitled4$ valgrind ./a.out 
==16288== Memcheck, a memory error detector
==16288== Copyright (C) 2002-2015, and GNU GPL'd, by Julian Seward et al.
==16288== Using Valgrind-3.11.0 and LibVEX; rerun with -h for copyright info
==16288== Command: ./a.out
==16288== 
Hello, World!
==16288== 
==16288== HEAP SUMMARY:
==16288==     in use at exit: 0 bytes in 0 blocks
==16288==   total heap usage: 4 allocs, 4 frees, 1,063 bytes allocated
==16288== 
==16288== All heap blocks were freed -- no leaks are possible
==16288== 
==16288== For counts of detected and suppressed errors, rerun with: -v
==16288== ERROR SUMMARY: 0 errors from 0 contexts (suppressed: 0 from 0)