Memory leak concepts - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ Predict Output

intermediate

Output of code with missing free() call

What is the output of this C program snippet?

C

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

int main() {
    int *ptr = malloc(sizeof(int));
    *ptr = 10;
    printf("%d\n", *ptr);
    // missing free(ptr);
    return 0;
}

A Compilation error

B 0

C 10

D Runtime error

💡 Hint

Think about what happens if you allocate memory but don't free it.

The program prints 10 because the allocated memory holds the value 10. Missing free() causes a memory leak but does not affect output here.

🧠 Conceptual

intermediate

Cause of memory leak in this code

Which line in the following code causes a memory leak?

C

#include <stdlib.h>

void func() {
    int *p = malloc(4 * sizeof(int));
    p = malloc(10 * sizeof(int));
    free(p);
}

A int *p = malloc(4 * sizeof(int));

B No memory leak

C free(p);

D p = malloc(10 * sizeof(int));

💡 Hint

Think about what happens to the first allocated memory.

The second malloc overwrites pointer p without freeing the first allocated memory, causing a memory leak.

🔧 Debug

advanced

Identify the memory leak in this function

What is the memory leak issue in this function?

C

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

char* create_string() {
    char *str = malloc(20);
    if (!str) return NULL;
    str = "Hello";
    return str;
}

A Memory allocated by malloc is overwritten by string literal assignment causing leak

B malloc size is too small

C Missing free(str) before return

D No memory leak, code is correct

💡 Hint

Look at what happens to the pointer after malloc.

The pointer str is assigned a string literal after malloc, losing the reference to allocated memory, causing a leak.

📝 Syntax

advanced

Which option causes a compile-time error?

Which of the following code snippets will cause a compile-time error?

A int *p = malloc(sizeof(int) * 5); p = NULL; free(p);

B int *p; free(p);

C int *p = malloc(sizeof(int) * 5); free(p);

D int *p = malloc(sizeof(int) * 5); free(p); free(p);

💡 Hint

Consider if the pointer is initialized before free.

Freeing an uninitialized pointer (C) causes undefined behavior and may cause compile or runtime errors depending on compiler and environment.

🚀 Application

expert

How many memory leaks occur in this program?

How many memory leaks occur when this program runs?

C

#include <stdlib.h>

int main() {
    int *a = malloc(10 * sizeof(int));
    int *b = malloc(5 * sizeof(int));
    a = b;
    free(b);
    return 0;
}

A 1

B 0

C 2

D 3

💡 Hint

Check which allocated memory is lost without free.

The original memory allocated to 'a' is lost when 'a' is assigned 'b' without freeing first, causing one memory leak.