Read from file or stdin

Question

I am writing a utility which accepts either a filename, or reads from stdin.

I would like to know the most robust / fastest way of checking to see if stdin exists (d

Answer 1

You can just read from stdin unless the user supply a filename ?

If not, treat the special "filename" - as meaning "read from stdin". The user would have to start the program like cat file | myprogram - if he wants to pipe data to it, and myprogam file if he wants it to read from a file.

int main(int argc,char *argv[] ) {
  FILE *input;
  if(argc != 2) {
     usage();
     return 1;
   }
   if(!strcmp(argv[1],"-")) {
     input = stdin;
    } else {
      input = fopen(argv[1],"rb");
      //check for errors
    }

If you're on *nix, you can check whether stdin is a fifo:

 struct stat st_info;
 if(fstat(0,&st_info) != 0)
   //error
  }
  if(S_ISFIFO(st_info.st_mode)) {
     //stdin is a pipe
  }

Though that won't handle the user doing myprogram

You can also check if stdin is a terminal/console

if(isatty(0)) {
  //stdin is a terminal
}