C Files

Read and write files.

❮ Previous Next ❯

FILE *f = fopen("notes.txt", "w");: modes "r" read, "w" write, "a" append.
fprintf(f, ...) writes formatted text.
fgets(line, size, f) reads a line.
fclose(f) closes the file.

Always check that fopen did not return NULL.

Key Takeaways: C Files

Mastering C Files helps you write clean and reliable C code. Follow standard conventions, test edge cases, and keep logic simple. Try running the code example below and complete the exercises to build confidence.

C Files Code Example

#include <stdio.h>

int main() {
    FILE *f = fopen("notes.txt", "w");
    if (f == NULL) return 1;
    fprintf(f, "Learn C\nBuild fast programs\n");
    fclose(f);

    char line[100];
    f = fopen("notes.txt", "r");
    while (fgets(line, sizeof line, f)) {
        printf("> %s", line);
    }
    fclose(f);
    return 0;
}

Output