boost库中的program_options

本文基本从官方文档中摘录出来的，便于查看。

官方文档：https://www.boost.org/doc/libs/1_57_0/doc/html/program_options.html

Github:https://github.com/boostorg/program_options.git

简介

boost库时c++常用的工具库，地位仅次于c++标准库，Boost库的掌握是C++工程师的基本要求。

boost.program_options是用于命令行参数解析的，类似于optarg的作用，但是其还可以读取配置文件、环境变量。

优点：

1. 使用更容易。定义参数处理的语法简单,库自身很小，比如转换参数值到指定的类型和保存参数值到变量的事情都是自动处理。

2. 错误报告更友好。可报告错误的命令行参数，库能自动生成使用帮助，避免手工更新使用帮助导致的不一致。

3. 参数能从不同的地方读取，当命令行参数不能满足要求，需要改用配置文件或环境变量，这些功能都能支持，代码改动很小。

使用示例

示例1

只处理两个选项，一个无参和一个有整数参数

program_options/example/first.cpp

// Copyright Vladimir Prus 2002-2004.
// Distributed under the Boost Software License, Version 1.0.
// (See accompanying file LICENSE_1_0.txt
// or copy at http://www.boost.org/LICENSE_1_0.txt)

/* The simplest usage of the library.
 */

#include <boost/program_options.hpp>
namespace po = boost::program_options;

#include <iostream>
#include <iterator>
using namespace std;

int main(int ac, char* av[])
{
    try {
				/* 1. 使用options_description声明所有允许的选项.
         * add_options返回定义了的特殊代理对象operator(),
         * 参数是<选项名称，有关值得信息，选项描述>*/
        po::options_description desc("Allowed options");
        desc.add_options()
            ("help", "produce help message")
            ("compression", po::value<double>(), "set compression level")
        ;

      	/* variables_map用于存储选项值，并且可以存储任意类型的值。
      	 * 接下来调用store,parse_command_line以及notify，使vm
         * 包含所有的命令行中的选项。*/
        po::variables_map vm;        
        po::store(po::parse_command_line(ac, av, desc), vm);
        po::notify(vm);    

      	/* 最后根据需要使用这些选项，variables_map类使用时就像std::map，
      	 * 使用as来获取其中值。 */
        if (vm.count("help")) {
            cout << desc << "\n";
            return 0;
        }

        if (vm.count("compression")) {
            cout << "Compression level was set to " 
                 << vm["compression"].as<double>() << ".\n";
        } else {
            cout << "Compression level was not set.\n";
        }
    }
    catch(exception& e) {
        cerr << "error: " << e.what() << "\n";
        return 1;
    }
    catch(...) {
        cerr << "Exception of unknown type!\n";
    }

    return 0;
}

运行

$ bin/gcc/debug/first
Compression level was not set.
$ bin/gcc/debug/first --help
Allowed options:
  --help                 : produce help message
  --compression arg      : set compression level
$ bin/gcc/debug/first --compression 10
Compression level was set to 10.

示例2

选项值也可以用int类型之外的更复杂的类型，并且包含未知选项的处理。

example/options_description.cpp

// Copyright Vladimir Prus 2002-2004.
// Distributed under the Boost Software License, Version 1.0.
// (See accompanying file LICENSE_1_0.txt
// or copy at http://www.boost.org/LICENSE_1_0.txt)

#include <boost/program_options.hpp>

using namespace boost;
namespace po = boost::program_options;

#include <iostream>
#include <algorithm>
#include <iterator>
using namespace std;


// A helper function to simplify the main part.
template<class T>
ostream& operator<<(ostream& os, const vector<T>& v)
{
    copy(v.begin(), v.end(), ostream_iterator<T>(os, " "));
    return os;
}

int main(int ac, char* av[])
{
    try {
        int opt;
        int portnum;
        po::options_description desc("Allowed options");
        desc.add_options()
            ("help", "produce help message")
          	/* 首先指定变量(&opt)，读取参数后，opt中会存储参数值，
          	 * 如果没有指定此参数，我们指定默认为10 */
            ("optimization", po::value<int>(&opt)->default_value(10),
                  "optimization level")
            ("verbose,v", po::value<int>()->implicit_value(1),
                  "enable verbosity (optionally specify level)")
            ("listen,l", po::value<int>(&portnum)->implicit_value(1001)
                  ->default_value(0,"no"),
                  "listen on a port.")
          	/* 用户可以通过长参--include-path,或者短参-I,
          	 * 类型为vector，说明后面可以跟多个值 */
            ("include-path,I", po::value< vector<string> >(),
                  "include path")
            ("input-file", po::value< vector<string> >(), "input file")
        ;
				
        /* 指出所有未知值，都应转换为"input-file"选项的值。
         * 还要使用command_line_parser类来代替parse_command_line */
        po::positional_options_description p;
        p.add("input-file", -1);

        po::variables_map vm;
        po::store(po::command_line_parser(ac, av).
                  options(desc).positional(p).run(), vm);
        po::notify(vm);

        if (vm.count("help")) {
            cout << "Usage: options_description [options]\n";
            cout << desc;
            return 0;
        }

        if (vm.count("include-path"))
        {
            cout << "Include paths are: "
                 << vm["include-path"].as< vector<string> >() << "\n";
        }

        if (vm.count("input-file"))
        {
            cout << "Input files are: "
                 << vm["input-file"].as< vector<string> >() << "\n";
        }

        if (vm.count("verbose")) {
            cout << "Verbosity enabled.  Level is " << vm["verbose"].as<int>()
                 << "\n";
        }

        cout << "Optimization level is " << opt << "\n";

        cout << "Listen port is " << portnum << "\n";
    }
    catch(std::exception& e)
    {
        cout << e.what() << "\n";
        return 1;
    }
    return 0;
}

运行

$ bin/gcc/debug/options_description --help
Usage: options_description [options]
Allowed options:
  --help                 : produce help message
  --optimization arg     : optimization level
  -I [ --include-path ] arg : include path
  --input-file arg       : input file
$ bin/gcc/debug/options_description
Optimization level is 10
$ bin/gcc/debug/options_description --optimization 4 -I foo -I another/path --include-path third/include/path a.cpp b.cpp
Include paths are: foo another/path third/include/path
Input files are: a.cpp b.cpp
Optimization level is 4

示例3

配置文件和命令行组合使用，并且有隐藏选项。

examples/multiple_sources.cpp

// Copyright Vladimir Prus 2002-2004.
// Distributed under the Boost Software License, Version 1.0.
// (See accompanying file LICENSE_1_0.txt
// or copy at http://www.boost.org/LICENSE_1_0.txt)

/* Shows how to use both command line and config file. */

#include <boost/program_options.hpp>
namespace po = boost::program_options;


#include <iostream>
#include <fstream>
#include <iterator>
using namespace std;

// A helper function to simplify the main part.
template<class T>
ostream& operator<<(ostream& os, const vector<T>& v)
{
    copy(v.begin(), v.end(), ostream_iterator<T>(os, " ")); 
    return os;
}


int main(int ac, char* av[])
{
    try {
        int opt;
        string config_file;
    
        // Declare a group of options that will be 
        // allowed only on command line
        po::options_description generic("Generic options");
        generic.add_options()
            ("version,v", "print version string")
            ("help", "produce help message")
            ("config,c", po::value<string>(&config_file)->default_value("multiple_sources.cfg"),
                  "name of a file of a configuration.")
            ;
    
        // Declare a group of options that will be 
        // allowed both on command line and in
        // config file
        po::options_description config("Configuration");
        config.add_options()
            ("optimization", po::value<int>(&opt)->default_value(10), 
                  "optimization level")
            ("include-path,I", 
                 po::value< vector<string> >()->composing(), 
                 "include path")
            ;

        // Hidden options, will be allowed both on command line and
        // in config file, but will not be shown to the user.
        po::options_description hidden("Hidden options");
        hidden.add_options()
            ("input-file", po::value< vector<string> >(), "input file")
            ;

        
        po::options_description cmdline_options;
        cmdline_options.add(generic).add(config).add(hidden);

        po::options_description config_file_options;
        config_file_options.add(config).add(hidden);

        po::options_description visible("Allowed options");
        visible.add(generic).add(config);
        
        po::positional_options_description p;
        p.add("input-file", -1);
        
        po::variables_map vm;
        store(po::command_line_parser(ac, av).
              options(cmdline_options).positional(p).run(), vm);
        notify(vm);
        
        ifstream ifs(config_file.c_str());
        if (!ifs)
        {
            cout << "can not open config file: " << config_file << "\n";
            return 0;
        }
        else
        {
            store(parse_config_file(ifs, config_file_options), vm);
            notify(vm);
        }
    
        if (vm.count("help")) {
            cout << visible << "\n";
            return 0;
        }

        if (vm.count("version")) {
            cout << "Multiple sources example, version 1.0\n";
            return 0;
        }

        if (vm.count("include-path"))
        {
            cout << "Include paths are: " 
                 << vm["include-path"].as< vector<string> >() << "\n";
        }

        if (vm.count("input-file"))
        {
            cout << "Input files are: " 
                 << vm["input-file"].as< vector<string> >() << "\n";
        }

        cout << "Optimization level is " << opt << "\n";                
    }
    catch(exception& e)
    {
        cout << e.what() << "\n";
        return 1;
    }    
    return 0;
}

对于在命令行和配置文件中都指定了相同的值。通常，首选先存储的值，可以通过优化代码来选择。

# example/multiple_sources.cfg
#
# Comment out this line to use hard-coded default value of 10
# 
optimization = 1
include-path = /opt

$ bin/gcc/debug/multiple_sources
Include paths are: /opt
Optimization level is 1
$ bin/gcc/debug/multiple_sources --help
Allows options:

Generic options:
  -v [ --version ]       : print version string
  --help                 : produce help message

Configuration:
  --optimization n       : optimization level
  -I [ --include-path ] path : include path

$ bin/gcc/debug/multiple_sources --optimization=4 -I foo a.cpp b.cpp
Include paths are: foo /opt
Input files are: a.cpp b.cpp
Optimization level is 4

来源：CSDN

作者：无名小卒～

链接：https://blog.csdn.net/sinat_36544290/article/details/104611616