parsing main

[acorn]

giving the function main

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

can someone show me how to parse commands passed through main. also how do i test it ? do run the command line in windows then the command along with the exe name?

[jsmith]

If the name of your executable is "foo" and the command-line you typed was

 foo 1 2 3 Hello 4 3.14 World

then

argv[0] is "foo"
argv[1] is "1"
argv[2] is "2"
argv[3] is "3"
argv[4] is "Hello"
argv[5] is "3.14"
argv[6] is "World"

and

argc is 7 (number of elements in the above array).

[acorn]

wow thats easy enough. thanks :)

[acorn]

maybe not so easy. its saying there is commands even when there isnt any. is there a default command also sent to main. everything seems like its one off. its also not recognizing string literals.

[Moschops]

Is the command that always seems to be there (I presume it's the string at argv[0]) the name of the executable?

[acorn]

ok its saying there is 1 command and then arg[0] is the string path up to main.

[acorn]

this doesnt work to well. at all. if i play with some options in the command prompt it does seem to pause to some commands but nothing happens. here is the code.

//removed long bad code 

[Moschops]

ok its saying there is 1 command and then arg[0] is the string path up to main.

By convention, that is always at least one command; the command used to run that actual executable.

[acorn]

yes. still wasnt able to get any commands working. any at all. can anyone provide a working sample of a parsed main with options. just something with a cout << printout you choosed option x.

[filipe]

#include <iostream>

int main(int argc, char** argv)
{
    if(argc < 2) {
        std::cerr << "Program requires one argument." << std::endl;
        return 1
    }
    else if(argc > 2) {
        std::cerr << "Too many arguments passed." << std::endl;
        return 2;
    }
    else {
        std::cout << argv[1] << std::endl;
    }
    return 0;
}

Try this.

[acorn]

thank flipe i see a few different things going on that was messing everything up. i thought you were suppose to pass the number of arguments along with the arguments themselves in the command line. this screws up what i wrote up above in a major way. thanks i can work on it from here.

[acorn]

your example worked with just echoing but when i try and actually parse it the command is there but the parsing isnt happening. like below.

if (argv[1] == "compress")
			std::cout << "compressing with default option";
		else
		{
			std::cout << argv[1]; // shows up as compress then why didnt the first if fire
			return 1;
		}

argv in the else is called and shows up as compress then why didnt the compress in the first half of the if statement fire.

[Zhuge]

Don't compare C-strings with ==, use strcmp().

[Moschops]

argv[1] is a character pointer. It has a value which is a numerical address; thus, you are testing a numerical address (i.e. a number) for equality to a string literal ("compress"). They are not going to be equal.

I suggest you use a comparison function, like strcmp.

[acorn]

ok that was the problem thanks guys. i learned tons with this exercise as aggravating as it was.

in the command line
typing main = program must require at least one argument
typing main compress = compressing with default option
typing main compress 1 = compressing with option 1
typing main compress 2 = compressing with option 2

#include <iostream>

int main(int argc, char** argv)
{
    if(argc < 2) {
        std::cerr << "Program requires one argument." << std::endl;
        return 1;
    }
    else if(argc == 2)
	{
		if ((std::strcmp(argv[1],"compress") == 0 ))
			std::cout << "compressing with default option";
		else
		{
			std::cout <<"unknown command";
			return 1;
		}
	}
    else if (argc == 3)
	{
		if (((std::strcmp(argv[1],"compress") == 0) && (std::strcmp(argv[2], "1") ==0 )))
                            std::cout << "compressing with option 1";
		else if (((std::strcmp(argv[1],"compress") == 0) && (std::strcmp(argv[2], "2") ==0 )))
                            std::cout << "compressing with option 2";
		else
		{
			std::cout << "unknown command sequence";
			return 1;
		}
    }

    return 0;
}