argc and argv in C++

Command line arguments in C++ using argc and argv

command_line_arguments_in_c++_using_argc_and_argv

In C++ it is possible to accept command line arguments. Command-line arguments are given after the name of a program in command-line operating systems like DOS or Linux, and are passed in to the program from the operating system. To use command line arguments in your program, you must first understand the full declaration of the main function, which previously has accepted no arguments. In fact, main can actually accept two arguments: one argument is number of command line arguments, and the other argument is a full list of all of the command line arguments.

The full declaration of main looks like this:

int main ( int argc, char *argv[] )

The integer, argc is the ARGument Count (hence argc). It is the number of arguments passed into the program from the command line, including the name of the program.

The array of character pointers is the listing of all the arguments. argv[0] is the name of the program, or an empty string if the name is not available. After that, every element number less than argc is a command line argument. You can use each argv element just like a string, or use argv as a two dimensional array. argv[argc] is a null pointer.

How could this be used? Almost any program that wants its parameters to be set when it is executed would use this. One common use is to write a function that takes the name of a file and outputs the entire text of it onto the screen.

#include <fstream>
#include <iostream>
 
using namespace std;
 
int main ( int argc, char *argv[] )
{
  if ( argc != 2 ) // argc should be 2 for correct execution
    // We print argv[0] assuming it is the program name
    cout<<"usage: "<< argv[0] <<" \n";
  else {
    // We assume argv[1] is a filename to open
    ifstream the_file ( argv[1] );
    // Always check to see if file opening succeeded
    if ( !the_file.is_open() )
      cout<<"Could not open file\n";
    else {
      char x;
      // the_file.get ( x ) returns false if the end of the file
      //  is reached or an error occurs
      while ( the_file.get ( x ) )
        cout<< x;
    }
    // the_file is closed implicitly here
  }
}

This program is fairly simple. It incorporates the full version of main. It first checks to ensure the user added the second argument, theoretically a file name. The program then checks to see if the file is valid by trying to open it. This is a standard operation that is effective and easy. If the file is valid, it gets opened in the process.


If you like dEexams.com and would like to contribute, you can also write your article here or mail your article to admin@deexams.com . See your article appearing on the dEexams.com main page and help others to learn.


Please write comments if you find anything incorrect, or you want to share more information about the topic discussed above.


Python if , elif and else

Python Conditions and If statements

  • 0
Python for beginners

Learning Python Part 1

  • 3
Struct Alignment and Padding

Struct Alignment and Padding in C++ And C

  • 0
Friend function

Friend function C++

  • 0
Pointers

C++ Pointers

  • 0
Structures

C++ Structures

  • 0
Types of Inheritance in C++

Inheritance and access specifiers C++

  • 0
Java date pattern

Java Date Pattern Syntax

  • 0
Java Date and Calendar

Java Date formats

  • 0
JAVA Data Type

Data types in Java

  • 0
Java unreachable code

Unreachable Code Error in Java

  • 0

Post Comment

Comments(0)

WEB TECHNOLOGY

Articles

×

Forgot Password

Please enter your email address below and we will send you information to change your password.