Question

Command line input

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 Linux and are passed in to the program from the operating system. To use command line arguments in the program, it must first understand the full declaration of the main function, which until now has accepted no arguments. In fact, main can 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 in an array of strings.

The full header 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. It can use each argv element just like a cstring or use argv as a twodimensional array.

How could this be used? Almost any program that wants its parameters to be set when it is executed would use this.

For example:

#include <iostream>

using namespace std;

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

// process command line arguments

cout << "The name of the program is " << argv[0] << endl;

if (argc == 1) {

cout << "Usage: Provide some command line arguments!\n";

} else {

cout << "The command line arguments are:\n";

for (int i = 1; i < argc; ++i) {

int value = std::atoi(argv[i]);

cout << argv[i];

if (value != 0) {

cout << " (value: " << value << ")\n";

}

cout << endl;

}

}

return 0;

}

This demonstration program is fairly simple. It first checks that the user added a second argument. The program checks to see if the argument is valid by trying to convert it using std::atoi.

The program gets the name of the file from the command line only. Do not interactively prompt the user for the file name.

• If no command line arguments are passed to the program, the program should display a usage message to the user and terminate.

• If more than 2 arguments are passed to the program, the program should display a usage message to the user and terminate.

A correct use would be:

./a.out file.txt

An incorrect use would be:

./a.out

Error: Specify the file name as a command line argument.

For example: ./a.out file1.txt

./a.out f1.txt f2.txt

Error: Specify the file name as a command line argument.

For example: ./a.out file1.txt

Answer 1

Please find the code below::::

#include <iostream>

using namespace std;

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

   // process command line arguments
   cout << "The name of the program is " << argv[0] << endl;
   if (argc <3) {
       cout << "Error: Specify the file name as a command line argument.";
       cout<<"\nFor example: ./a.out file1.txt file2.txt";
   }else if (argc > 3) {
       cout << "Error: Too many argument passed!!!,Specify the file name as a command line argument.";
       cout<<"\nFor example: ./a.out file1.txt file2.txt";
   }else {
       cout<<"File One name is : "<<argv[1]<<endl;
       cout<<"File Two name is : "<<argv[2]<<endl;

   }
   return 0;

}

command