Header File 

io.h  

Category 

Input/output Routines 

Prototype 

int _rtl_write(int handle, void *buf, unsigned len); 

Description 

Writes to a file.

The maximum number of bytes that _rtl_write can write is UINT_MAX -1 (because UINT_MAX is the same as -1), which is the error return indicator for _rtl_write. UINT_MAX is defined in limits.h. _rtl_write does not translate a linefeed character (LF) to a CR/LF pair because all its files are binary files. 

If the number of bytes actually written is less than that requested the condition should be considered an error and probably indicates a full disk. 

For disk files, writing always proceeds from the current file pointer. On devices, bytes are directly sent to the device. 

For files opened with the O_APPEND option, the file pointer is not positioned to EOF before writing the data. 

Return Value 

On success, _rtl_write returns number of bytes written.  

On error, it returns -1 and sets the global variable errno to one of the following values:

Example

#include <stdio.h>
#include <io.h>
#include <alloc.h>
#include <fcntl.h>
#include <process.h>
#include <sys\stat.h>
int main(void)
{
   void *buf;
   int handle, bytes;
   buf = malloc(200);
/* 
Create a file name TEST.$$$ in the current directory and writes 200 bytes to it. If TEST.$$$ already exists, it's overwritten.
 */
   if ((handle = open("TEST.$$$", O_CREAT | O_WRONLY | O_BINARY,
                       S_IWRITE | S_IREAD)) == -1)
   {
      printf("Error Opening File\n");
      exit(1);
   }
   if ((bytes = _rtl_write(handle, buf, 200)) == -1) {
      printf("Write Failed.\n");
      exit(1);
   }
   printf("_rtl_write: %d bytes written.\n",bytes);
   return 0;
}

Portability