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libargparse
===========
This is (yet another) simple command-line parser for C++ applications, inspired by Python's agparse module.
It requires only a C++11 compiler, and has no external dependancies.
One of the advantages of libargparse is that all conversions from command-line strings to program types (bool, int etc.) are performed when the command line is parsed (and not when the options are accessed).
This avoids command-line related errors from showing up deep in the program execution, which can be problematic for long-running programs.
Basic Usage
===========
```cpp
#include "argparse.hpp"
struct Args {
argparse::ArgValue<bool> do_foo;
argparse::ArgValue<bool> enable_bar;
argparse::ArgValue<std::string> filename;
argparse::ArgValue<size_t> verbosity;
};
int main(int argc, const char** argv) {
Args args;
auto parser = argparse::ArgumentParser(argv[0], "My application description");
parser.add_argument(args.filename, "filename")
.help("File to process");
parser.add_argument(args.do_foo, "--foo")
.help("Causes foo")
.default_value("false")
.action(argparse::Action::STORE_TRUE);
parser.add_argument(args.enable_bar, "--bar")
.help("Control bar")
.default_value("false");
parser.add_argument(args.verbosity, "--verbosity", "-v")
.help("Sets the verbosity")
.default_value("1")
.choices({"0", "1", "2"});
parser.parse_args(argc, argv);
//Show the arguments
std::cout << "args.filename: " << args.filename << "\n";
std::cout << "args.do_foo: " << args.do_foo << "\n";
std::cout << "args.verbosity: " << args.verbosity << "\n";
std::cout << "\n";
//Do work
if (args.do_foo) {
if (args.verbosity > 0) {
std::cout << "Doing foo with " << args.filename << "\n";
}
if (args.verbosity > 1) {
std::cout << "Doing foo step 1" << "\n";
std::cout << "Doing foo step 2" << "\n";
std::cout << "Doing foo step 3" << "\n";
}
}
if (args.enable_bar) {
if (args.verbosity > 0) {
std::cout << "Bar is enabled" << "\n";
}
} else {
if (args.verbosity > 0) {
std::cout << "Bar is disabled" << "\n";
}
}
return 0;
}
```
and the resulting help:
```
$ ./argparse_example -h
usage: argparse_example filename [--foo] [--bar {true, false}]
[-v {0, 1, 2}] [-h]
My application description
arguments:
filename File to process
--foo Causes foo (Default: false)
--bar {true, false}
Control whether bar is enabled (Default: false)
-v {0, 1, 2}, --verbosity {0, 1, 2}
Sets the verbosity (Default: 1)
-h, --help Shows this help message
```
By default the usage and help messages are line-wrapped to 80 characters.
Custom Conversions
==================
By default libargparse performs string to program type conversions using ``<sstream>``, meaning any type supporting ``operator<<()`` and ``operator>>()`` should be automatically supported.
However this does not always provide sufficient flexibility.
As a result libargparse also supports custom conversions, allowing user-defined mappings between command-line strings to program types.
If we wanted to modify the above example so the '--bar' argument accepted the strings 'on' and 'off' (instead of the default 'true' and 'false') we would define a custom class as follows:
```cpp
struct OnOff {
ConvertedValue<bool> from_str(std::string str) {
ConvertedValue<bool> converted_value;
if (str == "on") converted_value.set_value(true);
else if (str == "off") converted_value.set_value(false);
else converted_value.set_error("Invalid argument value");
return converted_value;
}
ConvertedValue<std::string> to_str(bool val) {
ConvertedValue<std::string> converted_value;
if (val) converted_value.set_value("on");
else converted_value.set_value("off");
return converted_value;
}
std::vector<std::string> default_choices() {
return {"on", "off"};
}
};
```
Where the `from_str()` and `to_str()` define the conversions to and from a string, and `default_choices()` returns the set of valid choices. Note that default_choices() can return an empty vector to indicate there is no specified default set of choices.
We then modify the ``add_argument()`` call to use our conversion object:
```cpp
parser.add_argument<bool,OnOff>(args.enable_bar, "--bar")
.help("Control whether bar is enabled")
.default_value("off");
```
with the resulting help:
```
usage: argparse_example filename [--foo] [--bar {on, off}] [-v {0, 1, 2}]
[-h]
My application description
arguments:
filename File to process
--foo Causes foo (Default: false)
--bar {on, off} Control whether bar is enabled (Default: off)
-v {0, 1, 2}, --verbosity {0, 1, 2}
Sets the verbosity (Default: 1)
-h, --help Shows this help message
```
Advanced Usage
==============
For more advanced usage such as argument groups see [argparse_test.cpp](argparse_test.cpp) and [argparse.hpp](src/argparse.hpp).
Future Work
===========
libargparse is missing a variety of more advanced features found in Python's argparse, including (but not limited to):
* action: append, count
* subcommands
* mutually exclusive options
* parsing only known args
* concatenated short options (e.g. `-xvf`, for options `-x`, `-v`, `-f`)
* equal concatenated option values (e.g. `--foo=VALUE`)
Acknowledgements
================
Python's [argparse module](https://docs.python.org/2.7/library/argparse.html)
|
