Creating Files

Creating and Opening Files

C reads and writes files with the FILE type and functions from <stdio.h>.

fopen

fopen opens (or creates) a file and returns a file pointer:

#include <stdio.h>

int main() {
    FILE *file = fopen("filename.txt", "w");
    if (file == NULL) {
        printf("Error opening file!\n");
        return 1;
    }
    fclose(file);
    return 0;
}

Modes

• "w" - write (creates or overwrites).
• "a" - append (writes at the end).
• "r" - read (file must exist).

Always check fopen's result

fopen returns NULL when it fails (file missing, no permission). Always check before using the file.

Closing

fclose flushes and closes the file at the end.

TL;DR

• fopen("name", "mode") opens/creates a file.
• Always check for NULL.
• fclose closes when done.
• Modes: "w" write, "a" append, "r" read.