Command Line Arguments in C++

Command-line arguments are arguments that are passed to a program when it is executed from the command line or terminal. They are provided in the command-line shell of operating systems with the program execution command.

The main function of C++ generally has the following signature:

int main(){
    
    // Function body
    return 0;
}

But to pass command-line arguments, we typically define main() with two arguments, where the first argument is the number of command-line arguments and the second is the list of command-line arguments.

Signature of main() Function for Command Line Arguments

int main(int argc, char *argv[]){
    
     // Function body
     return 0;
}

What is argc?

The variable argc (ARGument Count) is an integer that stores the number of command line arguments passed to the main function. It also includes the count for the name of the program, so if we pass a value to a program, the value of argc would be 2 (one for argument and one for program name).

What is argv?

The array argv (ARGument Vector) is an array of C-style strings like ('char*') where every element points to a command line argument. argv does not store the actual argument, but the pointer to that argument. The argv[0] will always contain the name of the program.

Example of Command Line Argument

#include <iostream>
using namespace std;

int main(int argc, char* argv[]) {
    cout << "You have entered " << argc
         << " arguments:" << endl;

    // Using a while loop to 
    // iterate through arguments
    int i = 0;
    while (i < argc) {
        cout << "Argument " << i + 1 
             << ": " << argv[i]
             << endl;
        i++;
    }

    return 0;
}

Input

./program1 hello geeks

Output

You have entered 3 arguments:
Argument 1: ./program1
Argument 2: hello
Argument 3: geeks

Command Line Arguments in Different Scenarios

The following programs illustrate the behaviour of C++ program for different kinds of command line arguments.

Multiple Command Line Arguments

In the following program, we pass three arguments to the main function from the command line.

#include <iostream>
using namespace std;

int main(int argc, char* argv[])
{
    if (argc >= 2) {

        // printing number of arguments
        cout << "Number Of Arguments Passed: " << argc
             << endl;
        cout << "----Following Are The Command Line "
                "Arguments Passed----"
             << endl;

        // printing all the arguments
        for (int i = 0; i < argc; ++i) {
            cout << "argv[" << i << "]: " << argv[i]
                 << endl;
        }
    }
    return 0;
}

Terminal Command:

$ ./program one two three

Output:

Number Of Arguments Passed: 4
----Following Are The Command Line Arguments Passed----
argv[0]: ./program
argv[1]: one
argv[2]: two
argv[3]: three

In the above program, the argv[0] points to the first command line argument and argv[argc-1] points to the last argument.

Note: Only string values are passed through the command line argument and argv[argc] is NULL.

Passing Space Seperated String as a Single Argument

In C++ program, multiple command line arguments are passed to the function by separating them by a whitespace but what happens if you have to pass an argument string that already contains spaces. In such case, we can enclose that string in the double quotes to pass it as a single argument.

#include <iostream>
using namespace std;

int main(int argc, char* argv[])
{
    cout << "Program Name Is: " << argv[0] << endl;

    if (argc >= 2) {
        cout << "Number Of Arguments Passed: " << argc
             << endl;
        cout << "----Following Are The Command Line "
                "Arguments Passed----"
             << endl;
        cout << "argv[0]: " << argv[0] << endl;
        cout << "argv[1]: " << argv[1] << endl;
    }

    return 0;
}

Terminal Command:

$ ./solution.out 'one two three'

Output:

Program Name Is: ./solution.out
Number Of Arguments Passed: 2
----Following Are The Command Line Arguments Passed----
argv[0]: ./solution.out
argv[1]: one two three

anuragvbj79

Follow

Improve

Article Tags :

• C++
• Geeks Premier League
• cpp-main
• Geeks Premier League 2023

Practice Tags :

• CPP