Command line argument types

I have class goto(speed), that takes double as an argument. What i would like to do is to allow user to set the speed when running the program from command line. The start of program would look like: program_name <file_name> <speed>. So argv[3] would be my speed but the problem is that argv arguments are passed as chars and i need a double. How can i solve this problem?

strtod().

http://www.google.com/search?q=strtod

strtod takes a string while argv[] is a pointer. How can i copy the value of argv[3] to some sort of string to pass it to strtod?

strtod() takes a C string, which is not a std::string. If you checked the prototype for strtod(), you would probably already know this. From the first hit in google:

Code:

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double strtod ( const char * str, char ** endptr );

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argv[3] is already in a position to be passed directly to strtod().

First of all i've read the reference, and second if that is so why does this come up with a segmentation fault?:

Code:

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double speed;

speed=strtod(argv[3], NULL);

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or even this:

Code:

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double speed;
char pend;

speed = strtod(argv[3], &pend)

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Probably because you're rushing to push argv[3] into it when in reality you need to check if argv[3] is even valid by way of argc (ie. if(argc > 3)....).

Besides, from what you described, you should be using argv[2].

You are right. What a stupid mistake. I should have used argv[2]. Thanks for your help MacGyver.

I would look into boost::lexical_cast, as well. Very handy C++-style stuff.

Thanks for your suggestion, but i need to have boost libraries for that and i wouldn't like to have any dependencies.

Boost is an excellent library and a must for any C++ programmer if you ask me.
There's no harm in dependencies. Most of boost are templates anyway, so it gets baked right into your code.
You could check the boost homepage for any goodies you might find.
Typical things might include boost::lexical_cast, boost::operators (boost::addable, boost::subtractable, etc), and much more.
Anyway, it's up to you.