Binary files and struct in C: solved exercise

Binary files and struct in C: solved exercise

This exercise is scheduled for daily publication and follows the same didactic structure used across the site: clear statement, compilable code, and expected output.

Problem statement

Implement a practical example of the topic and validate the output in the console.

C solution

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#include <stdio.h>

typedef struct {
    int id;
    char nombre[16];
} Alumno;

int main(void) {
    Alumno a = {1, "Ana"};
    FILE *f = fopen("alumnos.bin", "wb");
    if (!f) return 1;
    fwrite(&a, sizeof(Alumno), 1, f);
    fclose(f);

    Alumno b;
    f = fopen("alumnos.bin", "rb");
    if (!f) return 1;
    fread(&b, sizeof(Alumno), 1, f);
    fclose(f);

    printf("%d %s\n", b.id, b.nombre);
    return 0;
}

Expected output

1

1 Ana

Common mistakes

  • Not validating input and standard-library return values.
  • Ignoring edge cases (buffers, limits, null pointers).
  • Skipping basic compile/run verification.

Practical use

Binary files with structs are the foundation of proprietary data formats, simple databases, and efficient serialization.

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.