CODEWITHSUNDEEP
c++filec++11command-line
yxa0007
yxa0007

Reputation: 155

Sending text file name from command line c++

I want to run my code and send my file in 2 ways

  1. myprogram < input.txt or cat input.txt | myprogram
  2. myprogram input.txt

I have figured out the secong way using argc and argv[] but I am not able to figure out how to write the code for the first option. 

int main (int argc, char *argv[])
{
     ifstream fin;
     if(argc > 1){

        fin.open (argv[1]);
     }
     else
}

Upvotes: 0

Views: 807

Answers (2)

David C. Rankin
David C. Rankin

Reputation: 84521

As mentioned above in the comment, a portable way is passing either the open file or std::cin as an istream reference to a function and doing your input there. In that case either the file or std::cin may be passed. E.g.

#include <iostream>
#include <fstream>
#include <string>

void readinfo (std::istream& in)
{
    std::string s;
    while (in >> s)
        std::cout << s << '\n';
}

int main (int argc, char **argv) {

    if (argc > 1) {     /* read from file if given as argument */
        std::ifstream fin (argv[1]);
        if (fin.is_open())
            readinfo (fin);
        else {
            std::cerr << "error: file open failed.\n";
            return 1;
        }
    }
    else {  /* read from stdin */
        readinfo (std::cin);
    }

    return 0;
}

A non-portable Linux only option reading from /dev/stdin if no file is given simply requires a ternary operator, e.g.

    std::ifstream fin (argc > 1 ? argv[1] : "/dev/stdin");
    if (!fin.is_open()) {
        std::cerr << "error: file open failed.\n";
        return 1;
    }
    /* read from fin here */

Neither are completely elegant, but both support (subject to the OS constraint)

myprogram < input.txt

or 

myprogram input.txt

Upvotes: 5

xaviersjs
xaviersjs

Reputation: 1737

You want to read from stdin, and for that there's 2 options:

  • std::cin
  • fread() and other C-style IO

std::cin >> https://en.cppreference.com/w/cpp/io/cin has the advantage of reading formatted text into some binary representation https://en.cppreference.com/w/cpp/io/basic_istream/operator_gtgt

C-style IO https://en.cppreference.com/w/cpp/io/c has the advantage of reading binary data well.

It depends on what you want to do with it your input

Upvotes: -2

Related Questions