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Command Line Arguments

Started by NashuNatta Jun 15, 2004 at 9:08 AM 2 replies 600+ views

Original Post

Jun 15, 2004 at 9:08 AM

I have been having some trouble understanding the implementation of command line arguments. The tutorials that I read on google help, but can't realy answer my questions.


#include <iostream>
using namespace std;

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

Now from what I understand, the argc will check to see how many arguments are there, so if I were to type into my dos prompt app.exe -a -b -c it would see 3 arguments correct because the app itself doesnt count as an argument.Now, the argc is what is checking this right? Now, the big thing that I am having trouble comprehending is, is *argv[] checking what each of the commands is? For instance, say I had an app called math. The variables were set in the program to be 10 and 10. So say I called math.exe from my command prompt and added -a for add so... math.exe -a would come out to 20. How do I check within my program to see that I called -a? Is that were *argv[] comes in? This is what has been confusing me.

Monder

Jun 15, 2004 at 9:14 AM

Actually for app.exe -a -b -c argc would 4 (name used to invoke the application does count). char* argv[] is basically an array of char*s. Each of the char*s in the argv array points to a different argument, so in your math.exe -a example if you wanted to check for -a you would do something like

if(!strcmp("-a", argv[1])){  //add numbers}

Note it checks for -a against argv[1], argv[0] will contain the program name (math.exe).

Fruny

Jun 15, 2004 at 9:17 AM

The argv parameter is an array of C (null-terminated) strings (that is, char*). argv[0] is always the name of the executable itself. Then for each argument (delimited by spaces), the array contains one string. The [] indicates that the size of the array is not a-priory known.

So if you wanted to check that "-a" is in the argument list you would go like:

bool a_flag = false;int main(int argc, char* argv[]){   for(int i=1; i<argc; ++i)   {     if(!strcmp(argv, "-a")) a_flag = true;   }}

And then use the value of a_flag. Depending on your platform, you may actually have a library function that does command line parsing for you (e.g. getopt).

Jingo

Jun 15, 2004 at 9:22 AM

argv[0] can be "" as well as the name of the program ("" being an empty string).

argv[argc] is always zero.

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