CODEWITHSUNDEEP
cpointers
Calpurnius Kazik
Calpurnius Kazik

Reputation: 19

How to free memory of a char pointer inside a struct pointer

I'm able to assign values with strdup and print the values with this: (*test + index)->email but I have no idea how to free the memory allocated to the variable email. I thought about freeing test+index but I guess this would cause a memory leak, right? Taking into account that the struct has allocated memory and each of the pointer inside it have memory allocated with strdup.

Edit:

The code is roughly like this:

struct random {
    char *email;
} Random;

void function(Random **struct) {
    char *temp = calloc(100, sizeof(char));
    *struct = calloc(5, sizeof(Random));
    for (int i = 0; i < 5; i++) {
        scanf("%s", temp);
        (*struct + i)->email = strdup(temp); //This works
    }
    free((*struct + 3)->email); //Gives segmentation fault
}

int main() {
    Random *struct;

    function(&struct)
}

Upvotes: 1

Views: 252

Answers (3)

Jason Nguyen
Jason Nguyen

Reputation: 96

If I'm not mistaken, wouldn't it this?

free(*(test+index)->email);
free(text+index);

Upvotes: 1

chqrlie
chqrlie

Reputation: 144695

The posted code does not compile:

  • you cannot use struct as the name of a variable. struct is a keyword.
  • Random is a global variable, not a type.

It is idiomatic and much simpler in C to return the result instead of passing its address as an argument.

Following these remarks, and adding basic checks, the code should be simplified as:

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

typedef struct Random {
    char *email;
} Random;

Random *function(void) {
    char *temp = calloc(100, sizeof(char));
    if (temp == NULL)
        return NULL;
    Random *s = calloc(5, sizeof(Random));
    if (s != NULL) {
        for (int i = 0; i < 5; i++) {
            if (scanf("%99s", temp) != 1)
                *temp = '\0';
            (s + i)->email = strdup(temp); //This works
        }
        free((s + 3)->email); //Gives segmentation fault
    }
    free(temp);
    return s;
}

int main() {
    Random *s = function();
    // ...
}

This code, semantically equivalent to your posted fragment, does not have undefined behavior where you indicate, your actual code must be doing something else.

Upvotes: 1

user3629249
user3629249

Reputation: 16540

please read/understand: precedence of C operators

Then note that the de-reference operator * has a lower precedence than the + operator,

Therefore, The posted code needs to be modified to use something like:

(*mystruct)+i = ...

etc. Otherwise, the + will be executed before the *

Upvotes: 0

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