linecode/cxxopts

Lightweight C++ command line option parser

Quick start

This is a lightweight C++ option parser library, supporting the standard GNU style syntax for options.

Options can be given as:

--long
--long=argument
--long argument
-a
-ab
-abc argument

where c takes an argument, but a and b do not.

Additionally, anything after -- will be parsed as a positional argument.

Basics

#include <cxxopts.hpp>

Create a cxxopts::Options instance.

cxxopts::Options options("MyProgram", "One line description of MyProgram");

Then use add_options.

options.add_options()
  ("d,debug", "Enable debugging")
  ("f,file", "File name", cxxopts::value<std::string>())
  ;

Options are declared with a long and an optional short option. A description must be provided. The third argument is the value, if omitted it is boolean. Any type can be given as long as it can be parsed, with operator>>.

To parse the command line do:

auto result = options.parse(argc, argv);

To retrieve an option use result.count("option") to get the number of times it appeared, and

result["opt"].as<type>()

to get its value. If "opt" doesn't exist, or isn't of the right type, then an exception will be thrown.

Note that the result of options.parse should only be used as long as the options object that created it is in scope.

Exceptions

Exceptional situations throw C++ exceptions. There are two types of exceptions: errors defining the options, and errors when parsing a list of arguments. All exceptions derive from cxxopts::OptionException. Errors defining options derive from cxxopts::OptionSpecException and errors parsing arguments derive from cxxopts::OptionParseException.

All exceptions define a what() function to get a printable string explaining the error.

Help groups

Options can be placed into groups for the purposes of displaying help messages. To place options in a group, pass the group as a string to add_options. Then, when displaying the help, pass the groups that you would like displayed as a vector to the help function.

Positional Arguments

Positional arguments can be optionally parsed into one or more options. To set up positional arguments, call

options.parse_positional({"first", "second", "last"})

where "last" should be the name of an option with a container type, and the others should have a single value.

Default and implicit values

An option can be declared with a default or an implicit value, or both.

A default value is the value that an option takes when it is not specified on the command line. The following specifies a default value for an option:

cxxopts::value<std::string>()->default_value("value")

An implicit value is the value that an option takes when it is given on the command line without an argument. The following specifies an implicit value:

cxxopts::value<std::string>()->implicit_value("implicit")

If an option had both, then not specifying it would give the value "value", writing it on the command line as --option would give the value "implicit", and writing --option=another would give it the value "another".

Note that the default and implicit value is always stored as a string, regardless of the type that you want to store it in. It will be parsed as though it was given on the command line.

Boolean values

Boolean options have a default implicit value of "true", which can be overridden. The effect is that writing -o by itself will set option o to true. However, they can also be written with various strings using either =value or the next argument.

Custom help

The string after the program name on the first line of the help can be completely replaced by calling options.custom_help. Note that you might also want to override the positional help by calling options.positional_help.

Linking

This is a header only library.

Requirements

The only build requirement is a C++ compiler that supports C++11 regular expressions. For example GCC >= 4.9 or clang with libc++.

TODO list

• Allow unrecognised options.