C File handling

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File handling in C is crucial for tasks that involve storing data persistently on the disk. It allows you to create, read, write, and manipulate files. Here's a comprehensive guide to file handling in C, including examples for various file operations.

Common File Operations

1. Opening a File: Use fopen().

2. Reading from a File: Use functions like fgetc(), fgets(), and fscanf().

3. Writing to a File: Use functions like fputc(), fputs(), and fprintf().

4. Closing a File: Use fclose().

5. Positioning in a File: Use functions like fseek(), ftell(), and rewind().

Functions for File Handling

Opening a File: fopen()

To open a file, use the fopen() function.

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

Parameters:

• filename: The name of the file to open.

• mode: The mode in which to open the file.

File Modes:

Function Description
fopen() Opens a file
fprintf() Writes formatted data to a file
fscanf() Reads formatted data from a file
fputc() Writes a character to a file
fgetc() Reads a character from a file
fclose() Closes the file
fseek() Sets the file pointer to a given position
fputw() Writes an integer to a file
fgetw() Reads an integer from a file
ftell() Returns the current file position
rewind() Sets the file pointer to the beginning of the file
Mode Description
r Read mode (text file).
w Write mode (text file). Creates a new file or truncates an existing file.
a Append mode (text file). Adds to the end of an existing file.
r+ Read and write mode (text file).
w+ Read and write mode (text file). Creates or truncates the file.
a+ Read and write mode (text file). Appends to the end of the file.
rb Read mode (binary file).
wb Write mode (binary file).
ab Append mode (binary file).
rb+ Read and write mode (binary file).
wb+ Read and write mode (binary file).
ab+ Read and write mode (binary file). Appends to the end of the file.

Example:

#include <stdio.h>

int main() {
    FILE *fp;
    fp = fopen("example.txt", "w"); // Open file for writing
    if (fp == NULL) {
        perror("Error opening file");
        return -1;
    }
    fprintf(fp, "Hello, world!\\n");
    fclose(fp);
    return 0;
}

Closing a File: fclose()

To close a file, use the fclose() function.

int fclose(FILE *fp);

Reading from a File

#include <stdio.h>

int main() {
    FILE *fp = fopen("example.txt", "r");
    char ch;
    if (fp != NULL) {
        while ((ch = fgetc(fp)) != EOF) {
            putchar(ch);
        }
        fclose(fp);
    }
    return 0;
}

Writing to a File

#include <stdio.h>

int main() {
    FILE *fp = fopen("example.txt", "w");
    if (fp != NULL) {
        fputc('A', fp);
        fclose(fp);
    }
    return 0;
}

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