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

Below are a few of the features which cxxopts supports:

• Flags / Switches (i.e. bool fields)
  • Both short and long versions supported (i.e.-f and--flag respectively)
  • Supports combining short versions (i.e.-fBgoZ is the same as-f -B -g -o -Z)
  • Supports multiple occurrences (i.e.-vvv or-v -v -v)
  • Supports-?
• Positional Arguments
  • Supports the Unix-- meaning, only positional arguments follow
  • Supports partial parsing (i.e.cmd <options> sub-command <options> <positional>)
• Option Arguments (i.e. those that take values)
  • Both short and long versions supported (i.e.-o value,-ovalue and--option value or--option=value respectively)
  • Supports multiple values (i.e.-o <val1> -o <val2>)
  • Supports delimited values (i.e.--option=val1,val2,val3)
  • Supports custom parsers
  • Supports vector of vector values (i.e--opt=1,2,3 --opt=4,5,6)
• Groups
  • Arguments can be made part of a group for the purposes of displaying help messages
• Default Values
  • Supports default value from ENV variable
• Requirements
  • No external dependencies and only C++ 11 compatible compiler is required

Options can be given as:

--long--long=<argument>--long <argument>-a-ab-abc <argument>-c<argument>

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

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

#include<cxxopts.hpp>

Create acxxopts::options instance.

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

Then useadd_options.

options.add_options()  ("d,debug","Enable debugging")// a bool parameter  ("i,integer","Int param", cxxopts::value<int>())  ("f,file","File name", cxxopts::value<std::string>())  ("v,verbose","Verbose output", cxxopts::value<bool>()->default_value("false"))  ;

Options are declared with a long and an optional short option. A descriptionmust 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 useresult.count("option") to get the number of timesit appeared, and

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

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

Boolean options have a default implicit value of"true", which can beoverridden. The effect is that writing-o by itself will set optiono totrue. However, they can also be written with various strings using=value.There is no way to disambiguate positional arguments from the value followinga boolean, so we have chosen that they will be positional arguments, andtherefore,-o false does not work.

Parsing of list of values in form of anstd::vector<T> is also supported, as long asTcan be parsed. To separate single values in a list the ',' is used by default.Ensure that you use no whitespaces between values because those would be interpretedas the next command-line option. Example for a command-line optionthat can be parsed as astd::vector<double>:

--my_list=1,-2.1,3,4.5

To set up custom separation character (semicolon, for example) use:

cxxopts::value<std::vector<std::string>>()->delimiter(';')

When a parameter is not set, a value will be fetched from an environment variable (if such variable is defined).

cxxopts::value<int>()->env("MY_VAR")

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 specifiedon 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 thecommand 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 asthough it was given on the command line.

The same option can be specified several times, with different arguments, which will allbe recorded in order of appearance. An example:

--use train --use bus --use ferry

this is supported through the use of a vector of value for the option:

options.add_options()  ("use", "Usable means of transport", cxxopts::value<std::vector<std::string>>())

Positional arguments are those given without a preceding flag and can be usedalongside non-positional arguments. There may be multiple positional arguments,and the final positional argument may be a container type to hold a list of allremaining positionals.

To set up positional arguments, first declare the options, then configure aset of those arguments as positional like:

options.add_options()  ("script","The script file to execute", cxxopts::value<std::string>())  ("server","The server to execute on", cxxopts::value<std::string>())  ("filenames","The filename(s) to process", cxxopts::value<std::vector<std::string>>());options.parse_positional("script","server","filenames");// Parse options the usual wayoptions.parse(argc, argv);

For example, parsing the following arguments:

my_script.py my_server.com file1.txt file2.txt file3.txt

will result in parsed arguments like the following table:

You can allow unrecognised arguments to be skipped. This applies to bothpositional arguments that are not parsed into another option, and--arguments that do not match an argument that you specify. This is done bycalling:

options.allow_unrecognised_options();

and in the result object they are retrieved with:

result.unmatched()

Exceptional situations throw C++ exceptions. There are two types ofexceptions: errors defining the options and errors when parsing a list ofarguments. All exceptions derive fromcxxopts::option_error. Errorsdefining options derive fromcxxopts::spec_error and errorsparsing arguments derive fromcxxopts::parse_error.

All exceptions define awhat() function to get a printable stringexplaining the error.

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 toadd_options. Then,when displaying the help, pass the groups that you would like displayed as avector to thehelp function.

The string after the program name on the first line of the help can becompletely replaced by callingoptions.custom_help. Note that you mightalso want to override the positional help by callingoptions.positional_help.

template<>structcxxopts::value_parser<custom_type> {using value_type = custom_type;/// Is this a container type?staticconstexprbool is_container = <true> | <false>;voidparse(const cxxopts::parse_context& ctx,const std::string& text, custom_type& value) {// parse value from text here  }};

In case then a program has some global options and specific sets of optionsfor each subcommand, the following technique can be used.

Enable stop on the first positional feature:

options.stop_on_positional()

parse global options:

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

adjust values of argc and argv:

argc -= result.consumed();argv += result.consumed();

In the end, argv will point to the name of the subcommand.

Putting all together:

#include<cxxopts.hpp>intmain(int argc,char** argv) {  cxxopts::optionsoptions("test","A brief description");  options.add_options()    ("b,bar","Param bar", cxxopts::value<std::string>())    ("d,debug","Enable debugging", cxxopts::value<bool>()->default_value("false"))    ("f,foo","Param foo", cxxopts::value<int>()->default_value("10"))    ("h,help","Print usage");auto result = options.parse(argc, argv);if (result.count("help")) {    std::cout << options.help() << std::endl;exit(0);  }bool debug = result["debug"].as<bool>();  std::string bar;if (result.count("bar"))    bar = result["bar"].as<std::string>();int foo = result["foo"].as<int>();return0;}

Currently, there is no way to setup clang-format to format code beautifully with chained call operator. Consider to use initializer_list syntax:

options.add_options("group name", {  {"b,bar","Param bar", cxxopts::value<std::string>()},  {"d,debug","Enable debugging", cxxopts::value<bool>()->default_value("false")},  {"f,foo","Param foo", cxxopts::value<int>()->default_value("10")},  {"h,help","Print usage"}});

This is a header only library.

Note thatmaster is generally a work in progress, and you probably want to use atagged release version.