Boost parse_config_file,空键值

Question

我正在使用Boost program_options以标准方式解析配置文件,如
program_options的multiple_sources.cpp示例文件中所示.

    ifstream ini_file("config.ini");  
    po::store(po::parse_config_file(ini_file, desc, true), vm);  
    po::notify(vm);

但是config.ini文件具有空键=值对,例如:

key1=value1  
key2=value2  
key3=  
key4=  
key5=value5  

尝试读取此文件会导致Boost错误:

boost::program_options::invalid_option_value

boost :: program_options中是否有任何机制来读取具有空entires的配置文件？

任何帮助将非常感激.

---

我正在编辑这个问题,因为问题还没有解决.我将引用Boost(1.53)的例子.

这是完整的multiple_sources.cpp文件:

#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")
            //("optimization","optimization level")      
            ("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;
}

相应的配置文件(multiple_sources.cfg)是:

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

如果此文件现在修改为:

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

抛出以下错误消息:

the argument for option 'optimization' is invalid

所提出的具有验证重载等的解决方案似乎不必要地复杂化,特别是因为可能必须为每种数据类型编写验证函数,并且包含识别'\n'其他空白空间的可能性.

有什么建议？谢谢大家抽出时间.

---

根据Aditya的建议,我已经更换了以下内容:

            ("optimization", po::value<int>(&opt)->default_value(10), 
                  "optimization level")

以下内容:

            ("optimization", po::value<int>(&opt)->zero_tokens(), 
                  "optimization level")

并且:

            ("optimization", po::value<int>(&opt)->implicit_value(10), 
                  "optimization level")

他们都没有阅读空白选项.Boost示例程序"parser_test.cpp"通过将键值对读入向量来绕过使用zero_tokens()或implicit_value(),如下所示:

void test_config_file(const char* config_file)
{
    options_description desc;
    desc.add_options()
        ("gv1", new untyped_value)
        ("gv2", new untyped_value)
        ("empty_value", new untyped_value)
        ("plug*", new untyped_value)
        ("m1.v1", new untyped_value)
        ("m1.v2", new untyped_value)
        ("b", bool_switch())
    ;

    const char content1[] =
    " gv1 = 0#asd\n"
    "empty_value = \n"
    "plug3 = 7\n"
    "b = true\n"
    "[m1]\n"
    "v1 = 1\n"
    "\n"
    "v2 = 2\n"    
    ;

    vector<option> a2 = parse_config_file<char>(config_file, desc).options;
    BOOST_REQUIRE(a2.size() == 6);
    check_value(a2[0], "gv1", "0");
    check_value(a2[1], "empty_value", "");
    check_value(a2[2], "plug3", "7");
    check_value(a2[3], "b", "true");
    check_value(a2[4], "m1.v1", "1");
    check_value(a2[5], "m1.v2", "2");
}

Answer 1

我建议您用 try/catch 包围此异常，并仅对程序真正必需且不能为空的那些字段抛出错误，否则该字段将被忽略。