File Handling

ile handling in C allows your program to store data permanently on a hard drive. Without it, all your variables and data disappear the moment the program closes.

In C, we use a special pointer type called FILE * to interact with files.

The Basic Workflow

1. Open the file using fopen().

2. Check if the file actually opened (don't skip this!).

3. Process (Read from or Write to) the file.

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

int main() {
    FILE *fptr;
    char content[100];

    // --- WRITING TO A FILE ---
    fptr = fopen("example.txt", "w");

    if (fptr == NULL) {
        printf("Error opening file for writing!\n");
        return 1;
    }

    fprintf(fptr, "Hello, C File Handling!");
    fclose(fptr); // Always close after writing
    printf("Data written successfully.\n");

    // --- READING FROM A FILE ---
    fptr = fopen("example.txt", "r");

    if (fptr == NULL) {
        printf("Error opening file for reading!\n");
        return 1;
    }

    // fgets reads a string until it hits a newline or the limit
    if (fgets(content, 100, fptr) != NULL) {
        printf("Content of file: %s\n", content);
    }

    fclose(fptr); // Always close after reading

    return 0;
}

Expected Output:

Data written successfully.
Content of file: Hello, C File Handling!

ModeMeaningDescription"w"WriteCreates a new file (or overwrites an existing one)."r"ReadOpens an existing file to read data."a"AppendAdds new data to the end of an existing file.

Pro-Tips for File Handling

• The "NULL" Check: Always check if your FILE * is NULL. If you try to write to a NULL pointer (e.g., if the file is locked or the disk is full), your program will crash.