mirror of https://github.com/jarro2783/cxxopts.git
318 lines
10 KiB
Markdown
318 lines
10 KiB
Markdown
<div align="center">
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[](https://github.com/jarro2783/cxxopts/actions/workflows/cmake.yml)
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[](https://conan.io/center/recipes/cxxopts)
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[](https://vcpkg.io/en/package/cxxopts)
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[](https://github.com/jarro2783/cxxopts/releases)
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[](https://github.com/jarro2783/cxxopts)
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[](https://github.com/fffaraz/awesome-cpp)
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[](https://formulae.brew.sh/formula/cxxopts)
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[](./LICENSE)
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</div>
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# Release versions
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Note that `master` is generally a work in progress, and you probably want to use a
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tagged release version.
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## Version 3 breaking changes
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If you have used version 2, there are a couple of breaking changes in version 3
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that you should be aware of. If you are new to `cxxopts` you can skip this
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section.
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The parser no longer modifies its arguments, so you can pass a const `argc` and
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`argv` and expect them not to be changed.
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The `ParseResult` object no longer depends on the parser. So it can be returned
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from a scope outside the parser and still work. Now that the inputs are not
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modified, `ParseResult` stores a list of the unmatched arguments. These are
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retrieved like follows:
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```cpp
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auto result = options.parse(argc, argv);
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result.unmatched(); // get the unmatched arguments
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```
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# Quick start
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This is a lightweight C++ option parser library, supporting the standard GNU
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style syntax for options.
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Options can be given as:
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--long
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--long=argument
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--long argument
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-a
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-ab
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-abc argument
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where c takes an argument, but a and b do not.
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Additionally, anything after `--` will be parsed as a positional argument.
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## Basics
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```cpp
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#include <cxxopts.hpp>
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```
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Create a `cxxopts::Options` instance.
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```cpp
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cxxopts::Options options("MyProgram", "One line description of MyProgram");
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```
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Then use `add_options`.
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```cpp
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options.add_options()
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("d,debug", "Enable debugging") // a bool parameter
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("i,integer", "Int param", cxxopts::value<int>())
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("f,file", "File name", cxxopts::value<std::string>())
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("v,verbose", "Verbose output", cxxopts::value<bool>()->default_value("false"))
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;
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```
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Options are declared with a long and an optional short option. A description
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must be provided. The third argument is the value, if omitted it is boolean.
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Any type can be given as long as it can be parsed, with operator>>.
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To parse the command line do:
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```cpp
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auto result = options.parse(argc, argv);
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```
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To retrieve an option use `result.count("option")` to get the number of times
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it appeared, and
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```cpp
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result["opt"].as<type>()
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```
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to get its value. If "opt" doesn't exist, or isn't of the right type, then an
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exception will be thrown.
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## Unrecognised arguments
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You can allow unrecognised arguments to be skipped. This applies to both
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positional arguments that are not parsed into another option, and `--`
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arguments that do not match an argument that you specify. This is done by
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calling:
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```cpp
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options.allow_unrecognised_options();
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```
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and in the result object they are retrieved with:
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```cpp
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result.unmatched()
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```
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## Exceptions
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Exceptional situations throw C++ exceptions. There are two types of
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exceptions: errors defining the options, and errors when parsing a list of
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arguments. All exceptions derive from `cxxopts::exceptions::exception`. Errors
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defining options derive from `cxxopts::exceptions::specification` and errors
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parsing arguments derive from `cxxopts::exceptions::parsing`.
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All exceptions define a `what()` function to get a printable string
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explaining the error.
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## Help groups
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Options can be placed into groups for the purposes of displaying help messages.
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To place options in a group, pass the group as a string to `add_options`. Then, when displaying the help, `help` by default prints help for all groups. If you want to only print help for a specific group, pass the groups that you would like displayed as a vector to the `help` function.
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## Positional Arguments
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Positional arguments are those given without a preceding flag and can be used
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alongside non-positional arguments. There may be multiple positional arguments,
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and the final positional argument may be a container type to hold a list of all
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remaining positionals.
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To set up positional arguments, first declare the options, then configure a
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set of those arguments as positional like:
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```cpp
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options.add_options()
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("script", "The script file to execute", cxxopts::value<std::string>())
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("server", "The server to execute on", cxxopts::value<std::string>())
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("filenames", "The filename(s) to process", cxxopts::value<std::vector<std::string>>());
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options.parse_positional({"script", "server", "filenames"});
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// Parse options the usual way
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options.parse(argc, argv);
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```
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Note : `parse_positional` defaults to replacing the positionals with the arguments provided in the function call. To append to the existing list of positionals, please use `cxxopts::PositionalMode::Append`.
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```cpp
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options.parse_positional("another_option", cxxopts::PositionalMode::Append);
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```
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For example, parsing the following arguments:
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~~~
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my_script.py my_server.com file1.txt file2.txt file3.txt
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~~~
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will result in parsed arguments like the following table:
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| Field | Value |
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| ------------- | ----------------------------------------- |
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| `"script"` | `"my_script.py"` |
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| `"server"` | `"my_server.com"` |
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| `"filenames"` | `{"file1.txt", "file2.txt", "file3.txt"}` |
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## Default and implicit values
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An option can be declared with a default or an implicit value, or both.
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A default value is the value that an option takes when it is not specified
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on the command line. The following specifies a default value for an option:
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```cpp
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cxxopts::value<std::string>()->default_value("value")
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```
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An implicit value is the value that an option takes when it is given on the
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command line without an argument. The following specifies an implicit value:
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```cpp
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cxxopts::value<std::string>()->implicit_value("implicit")
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```
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If an option had both, then not specifying it would give the value `"value"`,
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writing it on the command line as `--option` would give the value `"implicit"`,
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and writing `--option=another` would give it the value `"another"`.
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Note that if `option` has an implicit value, specifying `--option another` will not work. You must use `=` syntax - `--option=another` or `-o=another`(assumming `o` is a short name for the option). This is because no argument is required. Hence, there is no good way to determine if the next string is an argument to your option or a positional argument.
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Note that the default and implicit value is always stored as a string,
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regardless of the type that you want to store it in. It will be parsed as
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though it was given on the command line.
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Default values are not counted by `Options::count`.
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### Implicit values with disabled arguments
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You can specify an option for which an argument cannot be specified using below syntax.
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```cpp
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cxxopts::value<bool>()->implicit_value("true", cxxopts::ImplicitArgPolicy::Disabled)
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```
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In this case specifying option as `--option=<value>` is disallowed and will throw `specified_disabled_args` exception. Note that `--option value` is not supported for implicit values. It is treated as positional/unmatched.
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## Boolean values
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Boolean options have a default implicit value of `"true"`, which can be
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overridden. The effect is that writing `-o` by itself will set option `o` to
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`true`. However, they can also be written with various strings using `=value`.
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There is no way to disambiguate positional arguments from the value following
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a boolean, so we have chosen that they will be positional arguments, and
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therefore, `-o false` does not work.
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## `std::vector<T>` values
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Parsing a list of values into a `std::vector<T>` is also supported, as long as `T`
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can be parsed. To separate single values in a list the define symbol `CXXOPTS_VECTOR_DELIMITER`
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is used, which is ',' by default. Ensure that you use no whitespaces between values
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(unless the entire list is double quoted) because those would be interpreted as the
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next command line option. Example for a command line option
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that can be parsed as a `std::vector<double>`:
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~~~
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--my_list=1,-2.1,3,4.5
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~~~
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If the list of values is quoted, then spaces can be included. For example:
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~~~
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--my_list="review,memory sanitize,build help,reformat"
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~~~
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This will be parsed into `review`, `memory sanitize`, `build help`, and `reformat`.
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## Options specified multiple times
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The same option can be specified several times, with different arguments, which will all
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be recorded in order of appearance. An example:
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~~~
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--use train --use bus --use ferry
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~~~
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this is supported through the use of a vector of value for the option:
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~~~
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options.add_options()
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("use", "Usable means of transport", cxxopts::value<std::vector<std::string>>())
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~~~
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## Custom help
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The string after the program name on the first line of the help can be
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completely replaced by calling `options.custom_help`. Note that you might
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also want to override the positional help by calling `options.positional_help`.
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## Example
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Putting all together:
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```cpp
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#include <iostream>
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#include "cxxopts.hpp"
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int main(int argc, char** argv)
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{
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cxxopts::Options options("test", "A brief description");
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options.add_options()
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("b,bar", "Param bar", cxxopts::value<std::string>())
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("d,debug", "Enable debugging", cxxopts::value<bool>()->default_value("false"))
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("f,foo", "Param foo", cxxopts::value<int>()->default_value("10"))
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("h,help", "Print usage")
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;
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auto result = options.parse(argc, argv);
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if (result.count("help"))
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{
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std::cout << options.help() << std::endl;
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exit(0);
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}
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bool debug = result["debug"].as<bool>();
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std::string bar;
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if (result.count("bar"))
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bar = result["bar"].as<std::string>();
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int foo = result["foo"].as<int>();
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return 0;
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}
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```
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# Linking
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This is a header only library.
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# Requirements
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The only build requirement is a C++ compiler that supports C++11 features such as:
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* regex
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* constexpr
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* default constructors
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GCC >= 4.9 or clang >= 3.1 with libc++ are known to work.
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The following compilers are known not to work:
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* MSVC 2013
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