File Operations (I/O) in C

C represents files as streams of characters. File operations require using the FILE structure defined in <stdio.h>.

1. Opening and Closing Files

Use fopen() to open a stream and fclose() to release the system file handle:

FILE *fptr = fopen("data.txt", "w"); // Mode "w" opens file for writing (overwrites)
if (fptr == NULL) {
    // Always check for NULL pointer in case of file open failures
}
fclose(fptr);

Common modes: - "r": Read mode. File must exist. - "w": Write mode. Creates file or truncates/overwrites if it exists. - "a": Append mode. Writes data at the end of the file.

2. Reading and Writing Text Files

• fprintf(file, ...): Writes formatted text output to a file stream.
• fscanf(file, ...): Reads formatted data input from a file stream.
• fgets(buffer, size, file): Reads a full line of text safely.

#include <stdio.h>

int main() {
    // Writing data
    FILE *write_ptr = fopen("score.txt", "w");
    if (write_ptr != NULL) {
        fprintf(write_ptr, "Highscore: %d\n", 950);
        fclose(write_ptr);
    }

    // Reading data
    FILE *read_ptr = fopen("score.txt", "r");
    if (read_ptr != NULL) {
        char line[50];
        if (fgets(line, sizeof(line), read_ptr) != NULL) {
            printf("Read from file: %s", line);
        }
        fclose(read_ptr);
    }
    return 0;
}

3. Binary File Operations

For raw data blocks (like arrays or structs), use binary mode ("wb", "rb") with: - fwrite(ptr, size, count, file): Writes block to file. - fread(ptr, size, count, file): Reads block from file.