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

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);
}