Sets the default file translation mode for file I/O operations.


errno_t _set_fmode(
   int mode


The file translation mode desired: _O_TEXT or _O_BINARY.

Return Value

Returns zero if successful, an error code on failure. If mode is not _O_TEXT or _O_BINARY or _O_WTEXT, the invalid parameter handler is invoked, as described in Parameter Validation. If execution is allowed to continue, this function sets errno to EINVAL and returns EINVAL.


The function sets the _fmode global variable. This variable specifies the default file translation mode for the file I/O operations _open and _pipe.

_O_TEXT and _O_BINARY are defined in Fcntl.h. EINVAL is defined in Errno.h.


Routine Required header Optional header
_set_fmode <stdlib.h> <fcntl.h>, <errno.h>

For more compatibility information, see Compatibility.


// crt_set_fmode.c
#include <stdlib.h>
#include <stdio.h>
#include <fcntl.h>     /* for _O_TEXT and _O_BINARY */
#include <errno.h>     /* for EINVAL */
#include <sys\stat.h>  /* for _S_IWRITE */
#include <share.h>     /* for _SH_DENYNO */

int main()
   int mode, fd, ret;
   errno_t err;
   int buf[12] = { 65, 66, 67, 68, 69, 70, 71, 72, 73, 74,
                   75, 76 };
   char * filename = "fmode.out";

   err = _get_fmode(&mode);
   if (err == EINVAL)
      printf( "Invalid parameter: mode\n");
      return 1;
      printf( "Default Mode is %s\n", mode == _O_TEXT ? "text" :

   err = _set_fmode(_O_BINARY);
   if (err == EINVAL)
      printf( "Invalid mode.\n");
      return 1;

   if ( _sopen_s(&fd, filename, _O_RDWR | _O_CREAT, _SH_DENYNO, _S_IWRITE | _S_IREAD) != 0 )
      printf( "Error opening the file %s\n", filename);
      return 1;

   if (ret = _write(fd, buf, 12*sizeof(int)) < 12*sizeof(int))
      printf( "Problem writing to the file %s.\n", filename);
      printf( "Number of bytes written: %d\n", ret);

   if (_close(fd) != 0)
      printf("Error closing the file %s. Error code %d.\n",
             filename, errno);

   system("type fmode.out");
Default Mode is binary
A   B   C   D   E   F   G   H   I   J   K   L

See also

Text and Binary Mode File I/O