CODEWITHSUNDEEP
cstdin
zell
zell

Reputation: 10204

Unexpected behavior when reading input parameters from stdin

I am testing a program "myprog.c" that crashes if it runs with any input parameter: 

#include <stdlib.h>
int main(int argc, char * arg[]){
  if (argc > 1 ){
    abort();

  }
}

As expected, "./myprog.out abc" crashes. But then I tried to get inputs from a file: "./myprog.out < inputs.txt", where inputs.txt has a couple of words, the program does not crash. Why not?

Upvotes: 0

Views: 139

Answers (2)

Paul-Marie
Paul-Marie

Reputation: 1063

It's because argc is equal to 1, you can verifie it with the following code:

int     main(int argc, char * arg[])
{
    printf("argc = %i\n", argc);
    if (argc > 1 ) {
        abort();
    }
}

output:

argc = 1

it appear because you can't pass argument like it, if you do it with a < your program will interpret it like it provide from stdin (filedescriptor numero 0)

if you want to pass more argument than 1, do like it:

./a.out abc def ghi

if you want get "argument" by a file, use a getline

Upvotes: 1

Some programmer dude
Some programmer dude

Reputation: 409176

That's because the shell doesn't pass < inputs.txt as arguments. Instead the shell makes it so that the contents of inputs.txt is to be read from stdin.

Upvotes: 2

Related Questions