Determines whether a file descriptor is associated with a character device.

  
      int _isatty(  
int fd   
);  

fd
File descriptor that refers to the device to be tested.

_isatty returns a nonzero value if the descriptor is associated with a character device. Otherwise, _isatty returns 0.

The _isatty function determines whether fd is associated with a character device (a terminal, console, printer, or serial port).

This function validates the fd parameter. If fd is a bad file pointer, the invalid parameter handler is invoked, as described in Parameter Validation. If execution is allowed to continue, the function returns 0 and sets errno to EBADF.

For more compatibility information, see Compatibility.

All versions of the C run-time libraries.

// crt_isatty.c  
/* This program checks to see whether  
 * stdout has been redirected to a file.  
 */  
  
#include <stdio.h>  
#include <io.h>  
  
int main( void )  
{  
   if( _isatty( _fileno( stdout ) ) )  
      printf( "stdout has not been redirected to a file\n" );  
   else  
      printf( "stdout has been redirected to a file\n");  
}  

stdout has not been redirected to a file  

File Handling