This article will give you in-depth information about the command line in C++ with uses and implementation.
The name is given after the name of the program in the command-line shell of Operating Systems. Whenever we write a program and run it into, we want some values to be input from the command line itself. These input values are called command-line values. It is handled using the main function.
Example
int main( int argc, char *argv[] )
argc - Number of arguments passed
argv[] - A pointer array which points to each argument passed in the program
Example:
Let us run this code on our Linux machine.
// Name of program commandline.cpp
#include <iostream>
using namespace std;
int main( int argc, char* argv[] )
{
cout << "You have entered " << argc
<< " arguments:" << "\n";
for (int i = 0; i < argc; ++i)
cout << argv[i] << "\n";
return 0;
}
Input:
$ g++ commandline.cpp -o main
$ ./main coding is fun
Output:
You have entered 4 arguments:
./main
coding
is
Fun
Properties of Command-Line Arguments:
- They are passed to the 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] point the last argument.
Note: You pass all the arguments separated by a space, but if the argument itself has space then you can pass such arguments by putting them inside double quotes “or single quotes.”
Example
#include<stdio.h>
int main(int argc,char* argv[])
{
int counter;
printf("Program Name Is: %s",argv[0]);
if(argc==1)
printf("\nNo Extra Command Line Argument Passed Other Than Program Name");
if(argc>=2)
{
printf("\nNumber Of Arguments Passed: %d",argc);
printf("\n----Following Are The Command Line Arguments Passed----");
for(counter=0;counter<argc;counter++)
printf("\nargv[%d]: %s",counter,argv[counter]);
}
return 0;
}
Output in different scenarios:
- Without argument: When the above code is compiled and executed without passing any argument, it produces the following output.
$ ./a.out
Program Name Is: ./a.out
No Extra Command Line Argument Passed Other Than Programme Name
- Three arguments: When the above code is compiled and executed with three arguments, it produces the following output.
$ ./a.out First Second Third
Program Name Is: ./a.out
Number Of Arguments Passed: 4
Following Are The Command Line Arguments Passed
argv[0]: ./a.out
argv[1]: First
argv[2]: Second
argv[3]: Third
- Single Argument: When the above code is compiled and executed with a single argument separated by space but inside double quotes, it produces the following output.
$ ./a.out “First Second Third”
Programme Name Is: ./a.out
Number Of Arguments Passed: 2
Following are the Command Line arguments passed
argv[0]: ./a.out
argv[1]: First Second Third
- The single argument in quotes separated by space: When the above code is compiled and executed with a single argument separated by space but inside single quotes, it produces the following output.
$ ./a.out ‘First Second Third’
Program Name Is: ./a.out
Number Of Arguments Passed: 2
Following Are The Command Line Arguments Passed
argv[0]: ./a.out
argv[1]: First Second Third
getopt() Function
It is a function in C to pass command line arguments.
Return Value: The getopt() function returns different values:
- If the option takes a value, that value is a pointer to the external variable optarg.
- ‘-1’ if there are no more options to process.
- ‘?’ when there is an unrecognized option and it stores into external variable optopt.
- If an option requires a value (such as -f in our example) and no value is given, getopt normally returns? By placing a colon as the first character of the options string, getopt returns: instead of? when no value is given.
Generally, the getopt() function is called from inside of a loop’s conditional statement. The loop terminates when the getopt() function returns -1. A switch statement is then executed with the value returned by getopt() function.
Syntax:
getopt(int argc, char *const argv[], const char *optstring)
optstring is simply a list of characters,
each representing a single character option.Why don’t you check out Features & Data types in C++.
By Mansi Agarwal
