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C++ for C Coders & Data Structures

Lecture Notes by [email protected]

Command line processing

The most important function of C/C++ is main() function. It is mostly defined with a return type of int and without parameters :

int main() { /* ... */ }

We can also give command-line arguments in C and C++. Command-line arguments are given after the name of the program in command-line shell of Operating Systems. To pass command line arguments, we typically define main() with two arguments : first argument is the number of command line arguments and second is list of command-line arguments.

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

or

int main(int argc, char **argv) { /* ... */ }
  • argc (ARGument Count) is int and stores number of command-line arguments passed by the user including the name of the program. So if we pass a value to a program, value of argc would be 2 (one for argument and one for program name)
  • The value of argc should be non negative.
  • argv(ARGument Vector) is array of character pointers listing all the arguments.
  • If argc is greater than zero, the array elements from argv[0] to argv[argc-1] will contain pointers to strings. Argv[0] is the name of the program , After that till argv[argc-1] every element is command -line arguments.
// Name of program argcargv.cpp
#include <iostream>
using namespace std;

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

    for (int i = 0; i < argc; ++i)
        cout << argv[i] << endl;

    return 0;
}

Input:

$ g++ argcargv.cpp -o arg
$ ./arg command line args

Output:

You entered 4 arguments:
./arg
command
line
args

Properties of Command Line Arguments:

  • They are passed to main() function.
  • They are parameters/arguments supplied to the program when it is invoked.
  • They are used to control program from outside instead of hard coding those values inside the code.
  • argv[argc] is a NULL pointer.
  • argv[0] holds the name of the program.
  • argv[1] points to the first command line argument and argv[n] points last argument.

Note: You pass all the command line arguments separated by a space, but if argument itself has a space then you can pass such arguments by putting them inside double quotes “” or single quotes ”.

Reference:

https://www.geeksforgeeks.org/command-line-arguments-in-c-cpp/

One thing I know, I was blind but now I see. John 9:25