Day 8.md

day	title	description
8	File Operations	Covering File Operations, File Modes, Error Handling, and Standard Library Functions for File Handling

Day 8 - File Operations

File Operations

Opening a File

A file can be opened using the fopen() function, which returns a file pointer.

FILE* fp = fopen("example.txt", "r");

Reading from a File

Data can be read from a file using the fread() or fscanf() functions.

char buffer[100];
fread(buffer, sizeof(char), 100, fp);
// OR
fscanf(fp, "%s", buffer);

Writing to a File

Data can be written to a file using the fwrite() or fprintf() functions.

char* data = "Hello, World!";
fwrite(data, sizeof(char), strlen(data), fp);
// OR
fprintf(fp, "%s", data);

Closing a File

A file can be closed using the fclose() function.

fclose(fp);

File Modes

Text Mode

In text mode, files are opened in a way that allows for reading and writing text data.

FILE* fp = fopen("example.txt", "r");

Binary Mode

In binary mode, files are opened in a way that allows for reading and writing binary data.

FILE* fp = fopen("example.bin", "rb");

Error Handling in File Operations

Checking for Errors

Errors can be checked using the ferror function.

if (ferror(fp)) {
    printf("Error occurred while reading file\n");
}

Handling Errors

Errors can be handled using the perror function.

if (fopen("example.txt", "r") == NULL) {
    perror("Error opening file");
}

Standard Library Functions for File Handling

fopen()

Opens a file and returns a file pointer.
Syntax: fopen(path, mode);

The different modes available:

Mode	Description
r	Only read.
w	Only write. If the file does not exist, it will be created.
a	Only append. If the file does not exist, it will be created.
r+	Read and write. The file pointer is positioned at the beginning of the file.
w+	Read and write. The file pointer is positioned at the beginning of the file.
a+	Read and append. The file pointer is positioned at the end of the file.

FILE* fp = fopen("example.txt", "r");

fclose()

Closes a file.

fclose(fp);

fread()

Reads data from a file.
Syntax: fread(dest_var, size_of_char, no_of_characters, file_pointer);

char buffer[100];
fread(buffer, sizeof(char), 100, fp);

fwrite()

Writes data to a file.
Syntax: fwrite(src_var, size_of_char, no_of_characters, file_pointer);

char* data = "Hello, World!";
fwrite(data, sizeof(char), strlen(data), fp);

fscanf()

Reads formatted data from a file.
Syntax: fscanf(file_pointer, format_string, var1, var2, ...);

char* name;
int score;
fscanf(fp, "%s %d", name, &score);

fprintf()

Writes formatted data to a file.
Syntax: fprintf(file_pointer, format_string, var1, var2, ...);

char* name = "Slim Shady";
int score = 10;
fprintf(fp, "%s: %d\n", name, score);

fseek()

Moves the file pointer to a specified location.
Syntax: fwrite(file_pointer, offset_amount, position_code);

For position_code, we have 3 macros:

position_code	Description
SEEK_SET	Beginning of the file
SEEK_CUR	Current position in the file
SEEK_END	End of the file

fseek(fp, 0, SEEK_SET);     // Beginning of file
fseek(fp, 10, SEEK_SET);    // 10 positions after beginning
fseek(fp, 40, SEEK_CUR);    // 10 positions after current position (10+40=50)
fseek(fp, 0, SEEK_END);     // Ending of file
fseek(fp, -5, SEEK_END);    // 5 positions before ending of file

ftell()

Returns the current position of the file pointer. Comes in handy when you have to check number of character's in the file.

long pos = ftell(fp);

rewind()

Moves the file pointer to the beginning of the file.

rewind(fp);

Example

#include <stdio.h>

int main() {
    FILE* fp = fopen("example.txt", "w");
    if (fp == NULL) {
        perror("Error opening file");
        return 1;
    }
    char* data = "Hello, World!";
    fwrite(data, sizeof(char), strlen(data), fp);
    fclose(fp);
    return 0;
}