Parsing Command Line Arguments in C++? [closed]

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What is the best way of parsing command-line arguments in C++ if the program is specified to be run like this:

prog [-abc] [input [output]]

Is there some way of doing this built into the standard library, or do I need to write my own code?

Related:

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42 Answers
42

The suggestions for boost::program_options and GNU getopt are good ones.

However, for simple command line options I tend to use std::find

For example, to read the name of a file after a -f command line argument. You can also just detect if a single-word option has been passed in like -h for help.

#include <algorithm>

char* getCmdOption(char ** begin, char ** end, const std::string & option)
{
    char ** itr = std::find(begin, end, option);
    if (itr != end && ++itr != end)
    {
        return *itr;
    }
    return 0;
}

bool cmdOptionExists(char** begin, char** end, const std::string& option)
{
    return std::find(begin, end, option) != end;
}

int main(int argc, char * argv[])
{
    if(cmdOptionExists(argv, argv+argc, "-h"))
    {
        // Do stuff
    }

    char * filename = getCmdOption(argv, argv + argc, "-f");

    if (filename)
    {
        // Do interesting things
        // ...
    }

    return 0;
}

On thing to look out for with this approach you must use std::strings as the value for std::find otherwise the equality check is performed on the pointer values.

I hope it is okay to edit this response instead adding a new one, as this is based on the original answer. I re-wrote the functions slightly and encapsulated them in a class, so here is the code. I thought it might be practical to use it that way as well:

class InputParser{
    public:
        InputParser (int &argc, char **argv){
            for (int i=1; i < argc; ++i)
                this->tokens.push_back(std::string(argv[i]));
        }
        /// @author iain
        const std::string& getCmdOption(const std::string &option) const{
            std::vector<std::string>::const_iterator itr;
            itr =  std::find(this->tokens.begin(), this->tokens.end(), option);
            if (itr != this->tokens.end() && ++itr != this->tokens.end()){
                return *itr;
            }
            static const std::string empty_string("");
            return empty_string;
        }
        /// @author iain
        bool cmdOptionExists(const std::string &option) const{
            return std::find(this->tokens.begin(), this->tokens.end(), option)
                   != this->tokens.end();
        }
    private:
        std::vector <std::string> tokens;
};

int main(int argc, char **argv){
    InputParser input(argc, argv);
    if(input.cmdOptionExists("-h")){
        // Do stuff
    }
    const std::string &filename = input.getCmdOption("-f");
    if (!filename.empty()){
        // Do interesting things ...
    }
    return 0;
}

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