C File Handling Tutorial

1. Opening a File

To open a file, use the fopen function. The syntax is:

FILE *fopen(const char *filename, const char *mode);

Common modes include "r" (read), "w" (write), and "a" (append).

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#include <stdio.h>

int main() {
    FILE *file = fopen("example.txt", "w");  // Open file for writing
    if (file == NULL) {
        printf("File could not be opened\\n");
        return 1;
    }
    fclose(file);  // Close file
    return 0;
}

2. Reading from a File

You can read from a file using functions like fgetc, fgets, or fread. The simplest form is fgetc, which reads one character at a time:

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#include <stdio.h>

int main() {
    FILE *file = fopen("example.txt", "r");  // Open file for reading
    char ch;
    if (file == NULL) {
        printf("File could not be opened\\n");
        return 1;
    }
    while ((ch = fgetc(file)) != EOF) {  // Read character by character
        putchar(ch);  // Print the character
    }
    fclose(file);
    return 0;
}

3. Writing to a File

To write to a file, you can use fputc, fputs, or fwrite. Here's how to use fputs to write a string:

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#include <stdio.h>

int main() {
    FILE *file = fopen("example.txt", "w");  // Open file for writing
    if (file == NULL) {
        printf("File could not be opened\\n");
        return 1;
    }
    fputs("Hello, World!", file);  // Write to file
    fclose(file);
    return 0;
}

4. Closing a File

Once you're done with a file, close it using the fclose function:

int fclose(FILE *file);

It ensures all data is written and resources are released.

5. Checking for Errors

To check if a file operation is successful, you can use the feof and ferror functions:

if (feof(file)) {
    printf("End of file reached\\n");
} else if (ferror(file)) {
    printf("Error reading the file\\n");
}

6. Conclusion

File handling in C is straightforward but requires attention to details such as opening, reading, writing, and closing files. Always ensure to close a file after you're done with it to prevent data loss and resource leaks.