Redirection question

[aquesada at mtecv2.mty.itesm.mx]

From: roarment at faui09.informatik.uni-erlangen.de (Roberto Armenti)
Message-ID: <roarment.658423394 at faui09>

>Hi net-people,
> 
> perhaps someone out there can help me.
> 
> Is there a _portable_ way to recognize whether input comes from
> stdin or from another stream ?
> To make the problem clearer : i'm working on a programm that takes
> its input from stdin. If however someone chooses to redirect the input
> to a file, so that data is read from that file, how can I figure that
> out ( Prompting and so on should not occur in this case ) ???
> 
> The solution should at least work on UNIX _AND_ MS-DOS, so i'm looking for
> a _portable_ implementation.
> Help out there ?
> 	Thanks in advance
> 		Roberto
> 
> 
> 
> 
>    
      Try this, it ran under both MSDOS and Ultrix. Sorry i don't give
 a longer explanation but i'm in a rush.

                 ************************************
#include <stdio.h>

FILE *entrada={stdin};
char linea[255];

main(argc,argv)
char *argv[];
{
    if(argc>1)
         {
           if((entrada=fopen(argv[1],"r"))==NULL)
                 puts("file not found"),exit(1);
           printf("Reading from file: %s\n",argv[1]);
/* In here goes any other code you need to execute when reading from a file */
         }
     while(!feof(entrada))
           {
          fgets(linea,255,entrada);
          puts(linea);
           }
}


  *************************************
>From Monterrey, Mexico:
Antonio Quesada Duarte
aquesada at mtecv2.mty.itesm.mx