fwrite() — Write Items

Format

#include <stdio.h>
size_t fwrite(const void *buffer, size_t size, size_t count,
                 FILE *stream);

Language Level: ANSI

Threadsafe: Yes.

Description

The fwrite() function writes up to count items, each of size bytes in length, from buffer to the output stream.

Return Value

The fwrite() function returns the number of full items successfully written, which can be fewer than count if an error occurs.

When using fwrite() for record output, set size to 1 and count to the length of the record to obtain the number of bytes written. You can only write one record at a time when using record I/O.

The value of errno can be set to:

Value

Meaning

ECONVERT

A conversion error occurred.

ENOTWRITE

The file is not open for write operations.

EPAD

Padding occurred on a write operation.

EPUTANDGET

An illegal write operation occurred after a read operation.

ESTDERR

stderr cannot be opened.

ESTDIN

stdin cannot be opened.

ESTDOUT

stdout cannot be opened.

ETRUNC

Truncation occurred on I/O operation.

EIOERROR

A non-recoverable I/O error occurred.

EIORECERR

A recoverable I/O error occurred.

Example that uses fwrite()

This example writes NUM long integers to a stream in binary format.

#include  <stdio.h>
#define  NUM  100
 
int main(void)
{
   FILE *stream;
   long list[NUM];
   int numwritten;
   int i;
 
   stream = fopen("MYLIB/MYFILE", "w+b");
 
   /* assign values to list[] */
   for (i=0;  i<=NUM; i++)
       list[i]=i;
 
   numwritten = fwrite(list, sizeof(long), NUM, stream);
   printf("Number of items successfully written = %d\n", numwritten);
}

Related Information

• fopen() — Open Files
• fread() — Read Items
• <stdio.h>