How to Use fclose in C: Syntax, Example, and Tips

In C, use fclose(FILE *stream) to close an open file and free its resources. It takes a file pointer returned by fopen and returns 0 on success or EOF on failure.

Syntax

The fclose function closes a file opened by fopen. It takes one argument:

• FILE *stream: The pointer to the file to close.

It returns 0 if the file closes successfully, or EOF if there is an error.

c

int fclose(FILE *stream);

Example

This example opens a file for writing, writes a line, then closes the file using fclose. It checks if closing was successful.

c

#include <stdio.h>

int main() {
    FILE *file = fopen("example.txt", "w");
    if (file == NULL) {
        printf("Failed to open file.\n");
        return 1;
    }

    fprintf(file, "Hello, fclose!\n");

    if (fclose(file) == 0) {
        printf("File closed successfully.\n");
    } else {
        printf("Error closing file.\n");
    }

    return 0;
}

Output

File closed successfully.

Common Pitfalls

Common mistakes when using fclose include:

• Not checking if the file was opened successfully before calling fclose.
• Calling fclose on a NULL pointer, which causes undefined behavior.
• Forgetting to close files, which can cause resource leaks.
• Ignoring the return value of fclose, missing errors like write failures.

c

#include <stdio.h>

int main() {
    FILE *file = NULL;

    // Wrong: fclose on NULL pointer
    // fclose(file); // This causes undefined behavior

    file = fopen("test.txt", "r");
    if (file != NULL) {
        // Correct: fclose only if file opened
        if (fclose(file) == 0) {
            printf("File closed properly.\n");
        } else {
            printf("Error closing file.\n");
        }
    }

    return 0;
}

Output

File closed properly.

Quick Reference

• fclose(FILE *stream): Closes the file and frees resources.
• Returns 0 on success, EOF on error.
• Always check if fopen succeeded before calling fclose.
• Close every file you open to avoid resource leaks.

Key Takeaways

Always close files with fclose to free system resources.

Check that fopen succeeded before calling fclose.

fclose returns 0 on success and EOF on failure; always check it.

Never call fclose on a NULL or already closed file pointer.

Forgetting fclose can cause file corruption or resource leaks.