🚀 go-pugleaf

On 3 Sep 1995, Henk den Adel wrote:

> You can use the ioctl function. In order to see whether stdin has
> been redirected, i use the following code:
> 
> int redirected;
> 
> redirected = ((ioctl(0,0)&2) == 0);

Not every DOS C compiler supports the ioctl() call. This is portable 
between all major compilers:

/*
**  iscons()
**
**  A function to determine if a specified stream refers to the console.
**
**  Original Copyright 1988-1991 by Bob Stout as part of
**  the MicroFirm Function Library (MFL)
**
**  This subset version is hereby donated to the public domain.
*/

#include <stdio.h>
#include <dos.h>

#define BOOL(x) (!(!(x)))

int iscons(FILE *fp)
{
      union REGS regs;

      regs.x.ax = 0x4400;
      regs.x.bx = (unsigned)fileno(fp);
      intdos(&regs, &regs);
      if (0 == (regs.x.ax & 0x80))
            return 0;
      return BOOL(regs.x.ax & 0x13);
}

#ifdef TEST

int main(void)
{
      fprintf(stderr, "stdin is%s redirected\n",
            iscons(stdin) ? " not" : "");
      fprintf(stderr, "stdout is%s redirected\n",
            iscons(stdout) ? " not" : "");
}

#endif /* TEST */


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