CODEWITHSUNDEEP
c++command-linearguments
bruxisma
bruxisma

Reputation: 429

Commandline arguments not working - Skips over them completely

Alright, I'm trying to get arguments to work properly with a small test application. My code is below. I'm not too experienced at C++, so I'm not sure why when I launch test with -print (or --print) it automatically states "Not a valid option" and then finishes up.

#include <iostream>

int main(int argc, char* argv[])
{
    int option;
    option = 1;
    char* argument;
    argument = argv[option];
    while (option < argc)
    {
        if (argument == "-print")
        {
            std::cout << "Printing Extra Text";
        }
        else
        {
            std::cout << "Not a valid option" << std::endl;
        }
        option++;
    }
    std::cout << "Printing normal text" << std::endl;
    return 0;
}

Am I doing this right? Thanks in advance.

Upvotes: 3

Views: 1014

Answers (6)

DrHazzard
DrHazzard

Reputation: 221

There is another problems, when you read the argument. (with all necessary changes)

int main(int argc, char* argv[])
{
    int option;
    option = 1;
    char* argument;
    while (option < argc)
    {
        argument = argv[option];
        if (strcmp(argument, "-print") == 0)
        {
            std::cout << "Printing Extra Text";
        }
        else
        {
            std::cout << "Not a valid option" << std::endl;
        }
        option++;
    }
    std::cout << "Printing normal text" << std::endl;
    return 0;
}

Upvotes: 1

fbonnet
fbonnet

Reputation: 2299

The following line is at fault:

if (argument == "-print")

Here you're comparing pointers, not string values. Replace with:

if (strcmp(argument, "-print") == 0)

C/C++ behave differently than Java or C# regarding string handling. Strings are not a native type or object but just glorified pointers to arrays of chars.

Alternatively, and if your option list becomes more complicated, consider using a dedicated option parsing library such as Boost's Program_options. It will handle all the aspects including validation and user messages.

Upvotes: 8

Steve Folly
Steve Folly

Reputation: 8627

Your question states you also want to test for --print (two dashes), but your code doesn't check for that.

Also, you assign argument outside the loop, you will want to do that inside the loop otherwise you'll only be testing argument #1 each time around the loop.

Upvotes: 1

Uli Gerhardt
Uli Gerhardt

Reputation: 14001

It's been a while that I programmed in C++, but shouldn't one just use

std::string argument;

and then the comparison with == would work?

Upvotes: 2

Stefan
Stefan

Reputation: 43575

if (argument == "-print")

you can not compare strings like this!

Use strcmp() to compare strings.

Upvotes: 1

gak
gak

Reputation: 32803

You're comparing the memory address of the string "-print" to the memory address of argument. This won't work! Use strcmp() to compare string values. Instead of:

if (argument == "-print")

do

if (strcmp(argument, "-print") == 0)

Upvotes: 12

Related Questions