fwrite() in C (original) (raw)

Last Updated : 8 Jan, 2025

In C, **fwrite() is a built-in function used to write a block of data from the program into a file. It can write arrays, structs, or other data to files but is especially designed to write binary data in binary files.

**Example:

C `

#include <stdio.h>

int main() { FILE *fptr = fopen("gfg.bin", "wb");

int a[] = {1, 2, 3, 4, 5};
int n = sizeof(a) / sizeof(a[0]);

// Write array a[] into the file using fwrite
fwrite(a, sizeof(int), n, fptr);

fclose(fptr);
return 0;

}

The **gfg.bin will contain the following data (in binary form):

12345

**Explanation: In the given program, **fwrite() writes the integer array **a[] as raw binary data to the file **gfg.bin. It writes **n elements of size **sizeof(int) from the array **a to the file.

This article covers the syntax, uses and common examples of fwrite() functions in C.

Table of Content

Syntax of fwrite()
Examples of fwrite()

Syntax of fwrite()

fwrite() is a standard library function defined in ****<stdio.h>** header file in C.

**fwrite(a, size, count, fptr);

**Parameters:

**a: Name of the array to be written.
**size: Size of each element.
**count: Number of elements to be written.
**fptr: Pointer to the file.

**Return Value:

It returns the number of objects written successfully.

This return value is generally used to check whether the write operation was successful or not.

Examples of fwrite()

The following examples demonstrate use of fwrite() function in C programs.

Writing a String to a Text File

C `

#include <stdio.h> #include <string.h>

int main() { FILE *fptr = fopen("gfg.txt", "w");

// Create a string for write into the file
char s[] = "Hello, geeksforgeeks!";

// Wrtie the string into the file using fwrite
int n = fwrite(s, sizeof(char), strlen(s), fptr);

// Here we check whole file is written into file
if(strlen(s) == n){
    printf("String written successfully");
}

fclose(fptr);
return 0;

}

Output

String written successfully

Writing a Structure to a File

A structure to a file can be written by fwrite() function as the raw binary data.

C `

#include <stdio.h> #include <string.h>

// Create a struct for inserting typedef struct { int a; int b; char s[20]; }GfG;

int main() { FILE *fptr = fopen("gfg.bin", "wb");

GfG gfg = {1, 999, "GeeksforGeeks"};

// Wrtie the gfgHeader data into the file using fwrite.
int n = fwrite(&gfg, sizeof(gfg), 1, fptr);

// Check data written successfully.
if(n == 1){
    printf("Structure written successfully");
}
fclose(fptr);
return 0;

}

Output

Structure written successfully