🚀 go-pugleaf

tim@tim.src.utah.edu (Tim Ma) writes:
: 
: Is there anyone I can tell from within a C program whether the user has
: redirected the output to a file using DOS redirection (>)?  
: 

Use the ioctl and fileno functions to get the device/file parameters from
DOS.  For standard input, use

   stdinparms = ioctl(fileno(stdin),0);

Substitute 'stdout' for 'stdin' to get the same data for standard output.
The return value will have bit 7 = 0 if the handle associated with the
stream you pass to fileno is a device, or bit 7 = 1 if it's a file.  e.g. to
determine if stdin refers to a file, use something like

   isredirected = ioctl(fileno(stdin),0) & 0x0080; 

The above example will determine when stdin has been redirected to a file.
To determine when standard input or output has been redirected to a device
other than CON, you can examine the lower 3 bits of the ioctl return value.
When bit 7 = 0 (indicating that the handle refers to a device), the values
of the low order bits are

   bit 0:  1 if handle refers standard input device (CON)
   bit 1:  1 if handle refers standard output device (CON)
   bit 2:  1 if handle refers to null device (NUL)

For example, to determine if stdout has been redirected to a some other 
device (LPT1, AUX, etc.), assuming bit 7 is zero, use

   isotherdevice = !(ioctl(fileno(stdout),0) & 0x0001);

Note that you can determine only that the device is not CON (i.e. you can't
determine what device the handle actually refers to).

Bit 2 is especially useful if you don't wish to waste time writing output
to the NUL device.

Hope this helps!  Write me, e-mail, if you have more specific questions 
about this.

Carl Harris
ceharris@csugrad.cs.vt.edu
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