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coldDeath · Aug 20th, 2005, 12:01 PM

Command line arguments in C++

This small tutorial will guide you through command line arguments in C++. It assumes you have at least basic knowledge of C++. If there is something unclear in this tutorial, private message, e-mail or instant message me with the details in my profile.

What is a command line argument?
An argument that the operating system passes to the main function in a C++ program. When the program is run from a console.

How do I run a program from a console?
It depends on your Operating System (OS).

Windows:
Compile your C++ program to an executable, then put it in a folder that is in the environmental variables path. If you don't know what this is, don't worry, you can just put your program into the C:/ directory. Then once in place, you must open the MS DOS prompt, you can do this by going: Start>Run and type cmd and press enter. You can get to the run prompt by using the windows key + r. From here if it says C:/> then you can run your program by typing in the filename and pressing enter. You do not need to add the .exe ending onto it. If you don't see the C:/> prompt, don't worry. Just type in this command and hit return: cd C:/ , then it should look like C:/>.

Linux(recommended :p):
Open the terminal (if you don't know how to do that, then I don't think you should use linux

) cd to the directory with the source code in it. For example: cd /home/jack/cpp/myfile.cpp then to use the G++ compiler to compile it type: g++ myfile.cpp this then makes a file called a.out, you can rename it if you like. a.out is an executable, so you can run it by typing ./a.out. If you dont want to put the ./ in front you can put the a.out file into /usr/bin, that way you only have to type the filename to run the program.

Ok i can run my program now, how do i add arguments?
Simply, when you run your program type the filename then a space then the argument. The syntax is:
filename argument1 argument2
you can use as many argument as you like.

How do i let my program accept these arguments?
Follow the tutorial below

.

Tutorial
Ok, when you run a program with an argument, how do you let the operating system send it to the program? Well thats easy, you just have to give the main function two arguments. One of these is an integer variable that will contain the number of arguments, another is an array that holds all the different arguments.
Syntax of main function using arguments:

(Toggle Plain Text)

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

See, easy, now your program can access the array as usual, whenever you want to use the argument you just have to use the variable:

(Toggle Plain Text)

argv[index number of argument]

Remember: arrays indexes start at 0!

ok here is an example:

(Toggle Plain Text)

#include <iostream> 
using namespace std; 
int main(int argc, char *argv[]){ 
    int i; 
    i = 0; 
    cout<<"There were "<<argc<<" arguments.\n"; 
    cout<<"They were:\n";
    while(i != argc){
        cout<<argv[i]<<"\n";
        i += 1;
}
    return 0;
}

That program will tell you how many arguments you gave the program and it will say what the arguments were.

Here is a pratical example of using command line arguments:

(Toggle Plain Text)

#include <iostream>
#include <fstream> // file handling capabilities
using namespace std;
int main(int argc, char *argv[]){
    if (argc != 2){
        cout<<"please provide one argument\n";
}else{
        ifstream my_file(argv[1]);
        if (!my_file.is_open()){
            cout<<"File couldn't be opened\n";
}else {
            char x;
            while (my_file.get(x)){ //returns false when reaches EOF
                cout<< x;
}
            my_file.close();
}
}
    return 0;
}

It reads and displays the contents of the file that you put as the argument.

I hope you understand how command line arguments work and that you will use them in the future.
ColdDeath.

proghelper · Aug 20th, 2005, 2:17 PM

This is a very useful set of notes on the command line arguments. Well Done

_______________

Programming ( Assignment / Project ) Help

coldDeath · Aug 20th, 2005, 2:21 PM

thanks,
please can a mod or an admin change the title of this topic to something more appropriate, such as: C++ Command Line Arguments Tutorial.
Because at th moment it looks liek its a question requiring help

thanks.

DaWei · Aug 20th, 2005, 2:24 PM

Somewhat of an oversimplification, and probably belongs in the tutorial section. If you plan to write for a critical audience, I'd also suggest a spelling and grammar checker as a minimum. Sorry to seem critical, but one hopes it'll goad you in the proper direction. Writing is fun and builds credentials if you publish; editors are highly critical and rejections are the norm, not the exception.

coldDeath · Aug 20th, 2005, 2:28 PM

You cannot post in the tutorial section, a mod must move it there

Thanks for being critical, i like that, it helps m improve and make my work more readable and interesting. I see i have a few typos, but i can't see that there is anythign wrong with my grammar.

DaWei · Aug 20th, 2005, 2:45 PM

Quote:

Compile you C++ program

A grammar checker will catch that, a spell checker won't, despite the fact that it's actually just a typo.

coldDeath · Aug 20th, 2005, 2:54 PM

ok i see, thanks.
the edit button shouldn't dissappear >

Infinite Recursion · Aug 22nd, 2005, 9:07 AM

nice work.

Scorpions4ever · Aug 22nd, 2005, 11:42 AM

You might want to mention that argv[0] is the name of the program itself. Also, the code indentation might need some work

.

thomas41546 · Aug 22nd, 2005, 11:58 AM

coldDeath sweet tutorial,

it helped me understand how arguments work in c++.

Definitely going to save this somewhere on my C drive.

Aug 20th, 2005, 12:01 PM	#1
coldDeath Expert Programmer Join Date: Aug 2005 Location: UK Posts: 862 Rep Power: 4	Arguments in C++ Command line arguments in C++ This small tutorial will guide you through command line arguments in C++. It assumes you have at least basic knowledge of C++. If there is something unclear in this tutorial, private message, e-mail or instant message me with the details in my profile. What is a command line argument? An argument that the operating system passes to the main function in a C++ program. When the program is run from a console. How do I run a program from a console? It depends on your Operating System (OS). Windows: Compile your C++ program to an executable, then put it in a folder that is in the environmental variables path. If you don't know what this is, don't worry, you can just put your program into the C:/ directory. Then once in place, you must open the MS DOS prompt, you can do this by going: Start>Run and type cmd and press enter. You can get to the run prompt by using the windows key + r. From here if it says C:/> then you can run your program by typing in the filename and pressing enter. You do not need to add the .exe ending onto it. If you don't see the C:/> prompt, don't worry. Just type in this command and hit return: cd C:/ , then it should look like C:/>. Linux(recommended :p): Open the terminal (if you don't know how to do that, then I don't think you should use linux ) cd to the directory with the source code in it. For example: cd /home/jack/cpp/myfile.cpp then to use the G++ compiler to compile it type: g++ myfile.cpp this then makes a file called a.out, you can rename it if you like. a.out is an executable, so you can run it by typing ./a.out. If you dont want to put the ./ in front you can put the a.out file into /usr/bin, that way you only have to type the filename to run the program. Ok i can run my program now, how do i add arguments? Simply, when you run your program type the filename then a space then the argument. The syntax is: filename argument1 argument2 you can use as many argument as you like. How do i let my program accept these arguments? Follow the tutorial below . Tutorial Ok, when you run a program with an argument, how do you let the operating system send it to the program? Well thats easy, you just have to give the main function two arguments. One of these is an integer variable that will contain the number of arguments, another is an array that holds all the different arguments. Syntax of main function using arguments: (Toggle Plain Text) int main(int argc, char argv[]){ //code } int main(int argc, char argv[]){ //code } See, easy, now your program can access the array as usual, whenever you want to use the argument you just have to use the variable: (Toggle Plain Text) argv[index number of argument] argv[index number of argument] Remember: arrays indexes start at 0! ok here is an example: (Toggle Plain Text) #include <iostream> using namespace std; int main(int argc, char argv[]){ int i; i = 0; cout<<"There were "<<argc<<" arguments.\n"; cout<<"They were:\n"; while(i != argc){ cout<<argv[i]<<"\n"; i += 1; } return 0; } #include <iostream> using namespace std; int main(int argc, char argv[]){ int i; i = 0; cout<<"There were "<<argc<<" arguments.\n"; cout<<"They were:\n"; while(i != argc){ cout<<argv[i]<<"\n"; i += 1; } return 0; } That program will tell you how many arguments you gave the program and it will say what the arguments were. Here is a pratical example of using command line arguments: (Toggle Plain Text) #include <iostream> #include <fstream> // file handling capabilities using namespace std; int main(int argc, char argv[]){ if (argc != 2){ cout<<"please provide one argument\n"; }else{ ifstream my_file(argv[1]); if (!my_file.is_open()){ cout<<"File couldn't be opened\n"; }else { char x; while (my_file.get(x)){ //returns false when reaches EOF cout<< x; } my_file.close(); } } return 0; } #include <iostream> #include <fstream> // file handling capabilities using namespace std; int main(int argc, char argv[]){ if (argc != 2){ cout<<"please provide one argument\n"; }else{ ifstream my_file(argv[1]); if (!my_file.is_open()){ cout<<"File couldn't be opened\n"; }else { char x; while (my_file.get(x)){ //returns false when reaches EOF cout<< x; } my_file.close(); } } return 0; } It reads and displays the contents of the file that you put as the argument. I hope you understand how command line arguments work and that you will use them in the future. ColdDeath.

Aug 20th, 2005, 2:21 PM	#3
coldDeath Expert Programmer Join Date: Aug 2005 Location: UK Posts: 862 Rep Power: 4	thanks, please can a mod or an admin change the title of this topic to something more appropriate, such as: C++ Command Line Arguments Tutorial. Because at th moment it looks liek its a question requiring help thanks. __________________ Programming Tutorials - Linux Installation Guide - Learn Python - Learn C++ Got Slack? Join us at #programmingforums @ irc.freenode.net! My software never has bugs. It just develops random features.

Aug 20th, 2005, 2:24 PM	#4
DaWei Resident Grouch Join Date: Jun 2005 Posts: 6,453 Rep Power: 10	Somewhat of an oversimplification, and probably belongs in the tutorial section. If you plan to write for a critical audience, I'd also suggest a spelling and grammar checker as a minimum. Sorry to seem critical, but one hopes it'll goad you in the proper direction. Writing is fun and builds credentials if you publish; editors are highly critical and rejections are the norm, not the exception. __________________ Abstraction doesn't make it impossible to write bad code; it makes it possible to write superior code. Contributor's Corner: Grumpy on C++ Exceptions DaWei on Pointers

Aug 20th, 2005, 2:28 PM	#5
coldDeath Expert Programmer Join Date: Aug 2005 Location: UK Posts: 862 Rep Power: 4	You cannot post in the tutorial section, a mod must move it there Thanks for being critical, i like that, it helps m improve and make my work more readable and interesting. I see i have a few typos, but i can't see that there is anythign wrong with my grammar. __________________ Programming Tutorials - Linux Installation Guide - Learn Python - Learn C++ Got Slack? Join us at #programmingforums @ irc.freenode.net! My software never has bugs. It just develops random features.

Aug 20th, 2005, 2:54 PM	#7
coldDeath Expert Programmer Join Date: Aug 2005 Location: UK Posts: 862 Rep Power: 4	ok i see, thanks. the edit button shouldn't dissappear > __________________ Programming Tutorials - Linux Installation Guide - Learn Python - Learn C++ Got Slack? Join us at #programmingforums @ irc.freenode.net! My software never has bugs. It just develops random features.

Aug 20th, 2005, 2:17 PM	#2
proghelper Newbie Join Date: Jun 2005 Posts: 16 Rep Power: 0	This is a very useful set of notes on the command line arguments. Well Done _______________ Programming ( Assignment / Project ) Help

Aug 22nd, 2005, 9:07 AM	#8
Infinite Recursion Programming Guru Join Date: Jul 2004 Location: United States Posts: 3,467 Rep Power: 8	nice work. __________________ http://jasonpowers.net "There are a thousand hacking at the branches of evil to one who is striking at the root."

Aug 22nd, 2005, 11:42 AM	#9
Scorpions4ever Programmer Join Date: Jun 2005 Posts: 86 Rep Power: 4	You might want to mention that argv[0] is the name of the program itself. Also, the code indentation might need some work .

Aug 22nd, 2005, 11:58 AM	#10
thomas41546 Newbie Join Date: Aug 2005 Location: Alberta, Edmonton Posts: 16 Rep Power: 0	coldDeath sweet tutorial, it helped me understand how arguments work in c++. Definitely going to save this somewhere on my C drive. __________________ My website: http://68.149.191.84 Don't you wonder what this says? Make sure you strip the code, of "\n". (Toggle Plain Text) V293LCBJIGNhbid0IGJlbGlldmUgeW91IGFyZS ByZWFkaW5nIHRoaXMsIGdvb2Qgam9iIDopIGF uZCB2aXNpdCBteSB3ZWJzaXRlIGF0IGh0dHA6L y82OC4xNDkuMjAzLjE0NCwgaXRzIG5vdCBhbHdh eXMgdXAu

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Programming Forums > Application Development > C

Arguments in C++