fwrite

 

C

Language

Standard Library

Type support

Dynamic memory management

Error handling

Program utilities

Date and time utilities

Strings library

Algorithms

Numerics

Input/output support

Localization support

Thread support (C11)

Atomic operations (C11)

 

File input/output

Functions
File access
fopen freopen fclose fflush	fwide setbuf setvbuf
Direct input/output
fread
fwrite
Unformatted input/output
fgetc fgets fputc fputs getchar gets putchar puts ungetc	fgetwc fgetws fputwc fputws getwchar putwchar ungetwc
Formatted input/output
scanffscanfsscanf vscanfvfscanfvsscanf (C99)(C99)(C99) printffprintfsprintfsnprintf (C99) vprintfvfprintfvsprintfvsnprintf (C99)	wscanffwscanfswscanf vwscanfvfwscanfvswscanf (C99)(C99)(C99) wprintffwprintfswprintf vwprintfvfwprintfvswprintf
File positioning
ftell
fgetpos
fseek
fsetpos
rewind
Error handling
clearerr
feof
ferror
perror
Operations on files
remove
rename
tmpfile
tmpnam

 

Defined in header <stdio.h>
size_t fwrite( const void *buffer, size_t size, size_t count,                FILE *stream );		(until C99)
size_t fwrite( const void *restrict buffer, size_t size, size_t count,                FILE *restrict stream );		(since C99)

Writes count of objects in the given array buffer to the output stream stream. Objects are not interpreted in any way.

Parameters

buffer	-	pointer to the first object object in the array to be written
size	-	size of each object
count	-	the number of the objects to be written
stream	-	pointer to the output stream

Return value

The number of objects written successfully.

Example

fwrite with error checking

Run this code

#include <stdio.h>
#include <stdlib.h>
 
int main(void)
{
    // write buffer to file
    FILE *f1;
    char buffer[] = { 'x' , 'y' , 'z' };
    f1 = fopen("file.bin", "wb");
    int ret_code = fwrite(buffer, sizeof(char), sizeof(buffer), f1);
    if (ret_code < (int)sizeof(buffer))
       if (ferror(f1))
       {
          perror("fwrite()");
          fprintf(stderr,"fwrite() failed in file %s at line # %d\n", __FILE__,__LINE__-5);
          exit(EXIT_FAILURE);
       }
    fclose(f1);
 
    // read the same data and print it to the standard output
    FILE *f2;
    char rbuf[10];
    f2 = fopen("file.bin", "rb");
    const char* res = fgets(rbuf, sizeof(rbuf), f2);
    fclose(f2);
 
    if (res) { // points to rbuf on read success, NULL on failure
        puts(res);
    }
 
    return EXIT_SUCCESS;
}

Output:

xyz

See also

printffprintfsprintfsnprintf (C99)	prints formatted output to stdout, a file stream or a buffer (function)
fputs	writes a character string to a file stream (function)
fread	reads from a file (function)
C++ documentation for fwrite