C++ ArgParse: command line parsing made simple

C++ ArgParse is an open source header-only C++11 library for parsing the command line (argc, argv) in a typed manner.

Due to the core's heavy usage of template magic, the library can expose a very easy-to-use interface, so you as an application developer only have to care about the good stuff. Think Python's argparse.

The source code documentation and code coverage results can be found here: https://backraw.github.io/cppargparse

Build tests

Build requirements:

• gcc, clang, or msvc
• cmake

Linux

git clone https://github.com/backraw/cppargparse.git
cd cppargparse

mkdir build
cd build

cmake -DCMAKE_BUILD_TYPE=Profiling ..
make run_tests

Of course, you can use every generator that CMake supports like Ninja, etc.

Windows

• Create the build directory inside the project directory
• Run cmake -G"Visual Studio 14 Win64" -DCMAKE_BUILD_TYPE=Debug ..
• Open cppargparse.sln
• Build RUN_TESTS

Requires at least Visual Studio 2015. This is because of GTest, which cannot be compiled using Visual Studio 2013 (AFAIK).

Or simply use MinGW and do it the Linux way on Windows.

Code coverage

Coverage requirements:

• gcov
• lcov
• genhtml
• python3

Run make coverage inside the build directory. This will automatically execute make run_tests beforehand.

Source code documentation

Requirements:

• doxygen
• graphviz (the dot command)

Running doxygen Doxyfile inside the project directory will update docs/html.

Install

To install the library, run sudo make install inside the build directory.

The library interface

Please have a look at the examples.

You can mix traditional and callback arguments as you wish. The ArgumentParser class provides an interface for both and doesn't care which one you chose.

The core

All the magic is done via the typed cppargparse::argument struct. Each such struct definition must provide 3 static methods:

• T parse(cmd, position, cmdargs)
• T convert(cmd, position, cmdargs)
• const char *error_string(position)

Parameter definition:

• cmd represents the whole command line inside a std::vector<std::string>
• position represents the argument iterator position inside cmd
• cmdargs represents the command line argument struct object

The ArgumentParser class provides the get_option<T>(cmdarg), get_option<T>(cmdarg, default) and get_flag(cmdarg) methods for calling the actual type converter methods provided by the cppargparse::argument<T> structs.

Assume the following command line arguments have been passed: -t 3 -n "My Name" --enable

// -t 3
parse<int>(<cmd>, <argument iterator position 0>, <cmdargs>)
// calls and returns the value of
convert<int>(<cmd>, <argument iterator position 1>, <cmdargs>)
// which is the integer 3.


// -n "My Name"
parse<std::string>(<cmd>, <argument iterator position 2>, <cmdargs>)
// calls and returns the value of
convert<std::string>(<cmd>, <argument iterator position 3>, <cmdargs>)
// which is the string "My Name".


// --enable
// flags are checked only for their existence inside <cmd>,
// they don't provide any conversion methods.

Primitive numerical types

Let's look at the int type, for example:

template <>
struct argument<int>
{
    static int parse(cmd, position, cmdargs)
    {
        return numerical_argument<int>::convert(cmd, std::next(position), &wrap, "int");
    }

    static int convert(cmd, position, cmdargs)
    {
        return numerical_argument<int>::convert(cmd, position, &wrap, "int");
    }

    static int wrap(const std::string &s)
    {
        return std::stoi(s);
    }
};

All it does is the following:

• Call cppargparse::numerical_argument::parse<int>() (or ::convert<int>()) on a command line argument iterator position position
• Tell it to use cppargparse::argument<int>::wrap() as the conversion function

wrap() is needed, because std::stoi() (in the case of int) cannot be passed as a parameter, since it contains default parameters. wrap() just gets rid of them and makes the function "passable".

The cppargparse::numerical_argument struct wraps the actual convert-or-error mechanism:

template <typename T>
struct numerical_argument
{
    static T convert(cmd, position, numerical_converter, type_string)
    {
        if (position == cmd.cend())
        {
            throw errors::CommandLineOptionError(...)
        }

        try
        {
            return numerical_converter(*position);
        }

        catch (const std::invalid_argument &)
        {
            throw errors::CommandLineOptionError(...)
        }
        catch (const std::out_of_range &)
        {
            throw errors::CommandLineOptionError(...)
        }
    }

    static const std::string error_message(position, type_string)
    {
        ...
    }
}

cppargparse::numerical_argument::convert() calls numerical_converter with a string as the argument. numerical_converter can (currently) be one of the following:

Data type	Wrapped converter function	C++ ArgParse implementation
int	std::stoi	int.h
unsigned int	stou (custom implementation)	int.h
long	std::stol	long.h
long long	std::stoll	long.h
unsigned long	std::stoul	long.h
unsigned long long	std::stoull	long.h
float	std::stof	float.h
double	std::stod	double.h
long double	std::stold	double.h

String types

Currently only std::string is implemented as a string type:

static const std::string convert(cmd, position, cmdargs)
{
    if (position == cmd.cend())
    {
        throw errors::CommandLineOptionError(...);
    }

    return *position;
}

It just checks whether the end of the command line argumnents list has been reached. If so, thrown an error, if not, return the string value for position.

Vector types

Currently only std::vector<T> is implemented as a vector type:

template <typename T>
struct argument<std::vector<T>>
{
    static const std::vector<T> parse(cmd, position, cmdargs)
    {
        auto positions = get_option_positions(cmd, position, cmdargs);
        std::vector<T> values;

        for (auto position : positions)
        {
            // Use the underlying argument::convert() method and store the returned value
            values.emplace_back(argument<T>::convert(cmd, position, cmdargs));
        }

        return values;
    }


    static types::CommandLinePositions_t get_option_positions(cmd, position, cmdargs)
    {
        types::CommandLinePositions_t positions;

        for (auto current = std::next(position); current != cmd.end(); ++current)
        {
            if (algorithm::find_arg(cmdargs, *current) != cmdargs.cend())
            {
                break;
            }

            positions.emplace_back(current);
        }

        return positions;
    }
}

It collects all values tied to the argument and converts each value string to T.

Custom types

... todo ...