C++ 接受带有“-”符号的命令行参数

Question

I am new to c++ and trying to read command line arguments specified as below.

./helloworld -i input_file -o outputfile -s flag3 -t flag4

I tried hardcoding the flags by index as below

int main(int argc, char *argv[]) {
 // argv[1] corresponds to -i
 // argv[2] corresponds to input_file
 // argv[3] corresponds to -o
 // argv[4] corresponds to outputfile
 // argv[5] corresponds to -s
 // argv[6] corresponds to flag3
 // argv[7] corresponds to -t
 // argv[8] corresponds to flag4

}

Then i realized the order can be changed so I can't use hardcoded index, I used a unordered_map<string, string> to put the -i, -o, -s, -t as keys and inputfile, outputfile, flag3, flag4 as values.

This is working fine, but I was wondering is there any better way to do the same.

Answer 1

Oh my gosh. Okay, you can do this manually, and I'll show you some code. But please look at getopt(). It already helps you out quite a bit, but it takes a little to get used to.

But here's how you could code it manually:

int index = 1;
while (index < argc) {
    string cmnd = argv[index++];
    if (cmnd == "-i") {
        if (index >= argc) {
            usage();   // This should provide help on calling your program.
            exit(1);
        }
        inputFileName = argv[index++];
    }
    else if (cmnd == "-whatever") {
        // Continue to process all your other options the same way
    }
}

Now, this isn't how anyone does this. We use some version of getopt(). There's another one I like called getopt_long, I believe. You'll want to dig something up like that. Then I put my own wrapper around all of that so I can do some really cool things.

If you want to see the wrapper I use: https://github.com/jplflyer/ShowLib.git and look at the OptionHandler.h and.cpp. It's pretty cool. I think there's an example of how to use it somewhere.

But you need to know how it works under the hood, so for your first programs, maybe do it manually like I've shown you.

Answer 2

You can use a 3rdparty library to parsing commandline arguments.
For example: https://github.com/mirror/tclap