safe realloc in C: solved exercise

safe realloc in C: solved exercise

This exercise is scheduled for daily publication and follows the standard site structure: statement, solution, and expected output.

Problem statement

Resize a dynamic array and avoid memory loss when realloc fails.

C solution

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

int main(void) {
    int n = 4;
    int *a = (int *)malloc(n * sizeof(int));
    if (!a) return 1;

    for (int i = 0; i < n; i++) a[i] = i + 1;

    int new_n = 8;
    int *tmp = (int *)realloc(a, new_n * sizeof(int));
    if (!tmp) {
        free(a);
        return 1;
    }
    a = tmp;

    for (int i = n; i < new_n; i++) a[i] = i + 1;
    printf("a[7] = %d\n", a[7]);

    free(a);
    return 0;
}

Expected output

1

a[7] = 8

Common mistakes

  • Assigning realloc directly to the original pointer and losing the reference if it fails.
  • Not freeing memory on error paths.
  • Resizing without correctly updating the number of elements.

Practical use

Using realloc with a temporary variable is the safe pattern for resizing dynamic buffers without leaks on failure.

Guided practice and full book

If you want a complete path with progressive difficulty:

FAQ

Is this exercise useful for C exams and technical interviews?

Yes. It targets patterns that commonly appear in practice assignments, technical interviews, and C programming exams.

Where can I keep practicing with more solved C exercises?

In Programming in C in 100 Solved Exercises and C Exercises. Kindle Unlimited: View on Amazon.

How should I practice this exercise type to improve faster?

Start with small inputs, run edge cases (empty, one item, max capacity), then rewrite the solution from scratch without copying.