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macro-argparse-cpp

Programs need command line arguments. I cherish the time when argparse module in python make my life easier dealing with command line arguments, but sometimes god needs us coding in c++ instead.

There are plenty of command line argument parser in the c/c++ world, such as:

However, they are either too syntacticly ugly, too many zombie features that confusing, or casting types anywhere and brining in too much concept and overhead that complicates everything.

So I start design and write a command line parsing library myself. The command line parser is defined using C macros, hence has 'macro' in the name.

Design goal

  • keep code concise and informative
  • no explicit type casting
  • write less code
  • header files only

Requirements

a decent c++ compiler with c++11 support

Setup

run make and you'll get two header files in include, namely:

  • macro-argparse-plain.hh
  • macro-argparse-jquery.hh copy them along with all other header files in include to your project, and include one of the above file. The difference between the two files will be explained after.

HOW TO USE?

Example:

#include "macro-argparse-plain.hh"

DEF_ARGUMENT_CLASS(
	Argument,
	std::string,	name,		"zxytim",	OPTIONAL, OPT_SLH(-n, --name, "who to say"),
	std::string,	content,	"Bonjour",	OPTIONAL, OPT_SH(-c, "what to say"),
	int,			times,		1,			REQUIRED, OPT_LH(--times, "say how many times?"),
	bool,			decorate,	false,		OPTIONAL, OPT_SLWH(-d, --decorate, true, "decoreate the output")
	);

int main(int argc, char *argv[]) {
	Argument args;
	if (!args.parse_args(argc, argv))
		return 1;
	if (args.decorate)
		std::cout << "==================" << std::endl;
	for (int i = 0; i < args.times; i ++)
		std::cout << args.content << " " << args.name << "!" << std::endl;
	if (args.decorate)
		std::cout << "==================" << std::endl;

	return 0;
}

results:

Error: `--times' required but not specified.
Usage: ./simple --times INT:TIMES [-c STRING:CONTENT] [-d] [-n STRING:NAME]
Options:
  --times INT:TIMES say how many times?
  -c STRING:CONTENT what to say
  -d, --decorate    decoreate the output
  -n, --name STRING:NAME who to say

more examples in example directory, use make test to compile them.

Define a class

Format of defining an argument class:

	DEF_ARGUMENT_CLASS(ArgumentClassName, [<type, name, default_val, presence, option>, ...])

where

  • presence is one of OPTIONAL or REQUIRED
  • option should be a call to macro OPT_.

OPT_SPECIFIER format

	OPT_SPECIFIER([<SHORT and/or LONG>, <SWITCH_TO_VAL>, <HELP>])

where SPECIFIER is a permutation of subsets of 'SLWH', defining the behavior of certain option:

  • S: SHORT
  • L: LONG
  • W: SWITCH_TO
  • H: HELP subject to the contraint that there at least one of S or L should present. The order parameters of OPT_SPECIFIER the same as order of charaters in in SPECIFIER.

for example: OPT_SLH denotes that there are three paramters: short option, long option and help message. So OPT_SLH should be invoked like:

OPT_SLH(-l, --long-option, "this is help message")

some more examples:

OPT_LWH(--long-option, "witch_to_value", "this is help message")
OPT_HL("this is help message", --long-option)
OPT_L(--long-option)

Parse Arguments

call

	args.parse_args(argc, argv);

or use initializer

	Argument args(argc, argv);

and you are set.

Argument Accessing Style

There are two argument accessing style. One is 'plain', in which arguments are stored as a public member variable of the class:

	std::cout << args.alpha << std::endl;
	args.beta = "hello";

and the other one is 'jquery', which borrows the idea of how jquery handles getters and setters: a member function with no parameter is getter, and a member function with a parameter acts as setter, and return the class instance, so that you can call setters in a chain::

	std::cout << args.alpha() << std::endl;
	args.beta("hello").alpha(10).alpha("10").pi(3.1415926);

Furthermore, a generic setter set accessing arguments by string is also provided:

	args.set("alpha", 10).set("alpha", "11");

Note that, a fallback is that all names that the class originally used can not be used again as arguments.

Type Cast

As you can see, when you set the value to a argument, you can almost give any reasonable type and we'll do the type convertion automatically for you.

Useful Helper Functions

  • print_help(std::ostream &&os, std::string const &prog_name): print the help message to os
  • dump(std::ostream &&os), dump(std::string const &path): dump parameters
  • load(std::istream &&os), load(std::string const &path): load parameters
  • std::vector get_option_info() const: retrieve option definitions

Development

The project is undergoing its fast prototyping phase. Source code is not well-organized nor well-documented at this stage.

Any advice or question on the design or implementation techniques is warmly welcomed.