C File Handling

File handling is an important aspect of programming, allowing programs to read from and write to files on a computer's file system. In C programming language, file handling is accomplished using a set of functions that are defined in the stdio.h library. Here are some of the commonly used functions for file handling in C:

1. fopen(): opens a file and returns a pointer to a FILE structure, which can be used to access the file.

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

2. fclose(): closes a file that was previously opened with fopen().

int fclose(FILE *stream);

3. fread(): reads a block of data from a file into a buffer.

size_t fread(void *ptr, size_t size, size_t count, FILE *stream);

4. fwrite(): writes a block of data from a buffer to a file.

size_t fwrite(const void *ptr, size_t size, size_t count, FILE *stream);

5. fprintf(): writes a formatted string to a file.

int fprintf(FILE *stream, const char *format, ...);

6. fscanf(): reads formatted input from a file.

int fscanf(FILE *stream, const char *format, ...);

7. fgets(): reads a line of text from a file into a buffer.

char *fgets(char *str, int n, FILE *stream);

8. fputs(): writes a string to a file.

int fputs(const char *str, FILE *stream);

To use these functions, you first need to open the file using fopen(), which returns a pointer to a FILE structure. You can then use other functions like fread(), fwrite(), and fprintf() to read from or write to the file, depending on your needs. Once you are done using the file, you should close it using fclose().

Here's an example of how to read and write from a file in C:

#include <stdio.h>

int main() {
    // Open the file for writing
    FILE *file = fopen("data.txt", "w");
    if (file == NULL) {
        printf("Error opening file.\n");
        return 1;
    }
    
    // Write some data to the file
    fprintf(file, "Hello, world!\n");
    fprintf(file, "This is a test.\n");
    
    // Close the file
    fclose(file);
    
    // Open the file for reading
    file = fopen("data.txt", "r");
    if (file == NULL) {
        printf("Error opening file.\n");
        return 1;
    }
    
    // Read the data from the file and print it to the console
    char buffer[1024];
    while (fgets(buffer, 1024, file)) {
        printf("%s", buffer);
    }
    
    // Close the file
    fclose(file);
    
    return 0;
}

In this example, the program first opens a file named data.txt for writing using fopen() with the "w" mode. It then writes some data to the file using fprintf(). Once it is finished writing to the file, it closes the file using fclose().

The program then opens the same file for reading using fopen() with the "r" mode. It reads the data from the file using fgets() and prints it to the console using printf(). Once it is finished reading from the file, it closes the file using fclose().

This program would output:

Hello, world!
This is a test.