Question

Okay, for a homework assignment my professor wants us to write a program in C++ that converts from miles to km. I did all that, the program runs. However, he has this special way of calling the program:

The program’s usage options are based
on the NAME of the BINARY FILE. If
the program name is ‘km2miles’, the
program interprets the command line
argument as a kilometer value to
convert to miles. If the name is
‘miles2km’, then it interprets as
miles being converted to km. Since the
first command line argument, argv[0]
is always the program’s name, you can
use its value to decide which function
to call.

I only have 3 files in this project (he tells us to ONLY have these 3):
convert.cpp
distance.cpp
distance.h

Distance .h and .cpp have the different functions to convert Mi to Km and Vice Versa, the convert.cpp has the main function. However, the only way I know how to call this program (after compiling it) is to say:

./convert 10

Where 10 is the number to convert. He says it should be called like this:

$ km2miles 100

and

$ miles2km 60

I have no idea how to get the program to act differently by having a different name… especially when that name doesn’t even run the program! Help would be appreciated.

Answer 1

You can:

• specify a name when you build it, and build it twice
• on Windows: copy convert miles2kms; copy convert kms2miles
• on UNIX/Linux: cp convert miles2kms; cp convert kms2miles
• on UNIX/Linx (better): make a link or symbolic link: ln -s convert miles2kms; ln -s convert kms2miles.

Inside your program, you should be doing something like:

#include <string>
#include <iostream>

int main(int argc, const char* argv[])
{
    std::string program_name = argv[0];

    if (argc != 2) {
        std::cerr << "usage: " << program_name << " <value>\n";
        return 0;
    }
    if (/* TODO: what would go here? */)
        ...
    else
        ...
}