c++ - json数组映射问题与boost json解析器

Question

我在下面的代码片段中解析下面的示例文件。

{
    "requestType": "INVOCATION",
    "hostName": "localhost",
    "serviceName": "bucky",
    "serviceType": "DISCRETE",
    "serviceParameters": "sampleData",
    "servicesList": [{
        "serviceName": "ABC",
        "serviceParameters": {
            "para1": "value1",
            "para2": "value2",
            "para3": "value3"
        }
    },
    {
        "serviceName": "CBA",
        "serviceParameters": {
            "para1": "value90",
            "para2": "value",
            "para3": "value"
        }
    }],
    "dataTransferMode": null
}

代码片段:

#include <boost/foreach.hpp>
#include <boost/property_tree/json_parser.hpp>
#include <boost/property_tree/ptree.hpp>
#include <iostream>
#include <map>
#include <sstream>
using boost::property_tree::ptree;
using namespace std;

void print(boost::property_tree::ptree const &pt, vector<string> &service_list, map<string, string> &service_param) {
    using boost::property_tree::ptree;
    ptree::const_iterator end = pt.end();
    string value;
    for (ptree::const_iterator it = pt.begin(); it != end; ++it) {
        // cout<<it->first<<":"<<it->second.get_value<std::string>()<<endl;

        if (it->first == "serviceName") {
            value = it->second.get_value<std::string>();
            service_list.push_back(it->second.get_value<std::string>());
        }

        if (it->first == "para1") {

            service_param[it->first] = it->second.get_value<std::string>();
        }

        if (it->first == "para2") {
            service_param[it->first] = it->second.get_value<std::string>();
        }

        if (it->first == "para3") {
            service_param[it->first] = it->second.get_value<std::string>();
        }

        print(it->second, service_list, service_param);
    }
}

int main() {

    vector<string> service_list;
    map<string, string> service_param_rgbd;
    map<string, map<string, string> > map_name;
    std::ifstream file("sample");
    std::stringstream ss;

    if (file) {
        ss << file.rdbuf();
        cout << "done";
        file.close();
    }

    boost::property_tree::ptree pt;
    boost::property_tree::read_json(ss, pt);

    try {
        BOOST_FOREACH (boost::property_tree::ptree::value_type &v, pt.get_child("servicesList")) {
            assert(v.first.empty()); // array elements have no names
            print(v.second, service_list, service_param_rgbd);
        }

        for (auto itr : service_list) {

            cout << itr << endl;
        }

        for (auto itr : service_param_rgbd) {
            if (find(service_list.begin(), service_list.end(), "ABC") != service_list.end()) {
                map_name["ABC"][itr.first] = itr.second;
            }
        }

        for (auto &i : map_name) {

            for (auto &j : i.second) {
                cout << j.first << ":" << j.second << endl;
            }
        }

        return EXIT_SUCCESS;

    }

    catch (std::exception const &e) {
        std::cerr << e.what() << std::endl;
    }
    return EXIT_FAILURE
}

在上面的代码中，我需要填充 vector 和 map ，以便在服务名称和服务参数之间建立映射，并且对于同一个 map > 需要创建 map_name。

所以在循环本身的当前场景中，我想创建嵌套映射，以便我将映射服务名称和相应的参数。按照下面的代码片段，在外循环中 i->first 将迭代服务名称，内循环将为我提供相应的参数 (para1=>value1,para2=>value2) 。这样服务名称和相应的参数都可以绑定(bind)在一个映射中。

for (auto &i : map_name) {
    for (auto &j : i.second) {
        cout << j.first << ":" << j.second << endl;
    }
}

任何人都可以让我知道与这种方法相同的有效方法:

• (a) 需要为每个服务创建单独的嵌套 map 。
• (b) 两个服务名称的相同参数名称将不起作用，并且无法区分具有相同参数名称的不同 2 服务。

Answer 1

真正的问题是缺乏抽象。

简单地读入一个真实的数据结构:

struct service {
    std::string name;

    struct parameters_t {
        std::string para1, para2, para3;
    } parameters;
};

可以这么简单

for (auto& v : pt.get_child("servicesList"))
{
    auto& node = v.second;
    service svc;
    svc.name = node.get("serviceName", "");
    svc.parameters.para1 = node.get("serviceParameters.para1", "");
    svc.parameters.para2 = node.get("serviceParameters.para2", "");
    svc.parameters.para3 = node.get("serviceParameters.para3", "");

    if (!services.insert(svc).second)
        std::cout << "skipped duplicate service\n";
}

我更喜欢使用 Boost multi_index_container，这样我可以根据需要添加多个索引，但现在只需要按名称的索引:

using Table = bmi::multi_index_container<
    service,
    bmi::indexed_by<
        bmi::ordered_unique<bmi::tag<struct by_name>,
            bmi::member<service, std::string, &service::name>
        >
    >
>;

为 service 对象添加调试打印机:

static inline std::ostream& operator<<(std::ostream& os, service const& s) {
    return os << "'" << s.name << "' params { "
        << "'" << s.parameters.para1 << "' "
        << "'" << s.parameters.para2 << "' "
        << "'" << s.parameters.para3 << "' }";
}

这是完整的测试程序，经过简化:

int main() {
    Table services = read_json("input.txt");

    for (auto& itr : services) {
        std::cout << itr.name << "\n";
    }

    auto it = services.find("ABC");
    assert(it != services.end());
    auto const& abc = *it;

    std::cout << abc << "\n";
}

完整演示

Live On Coliru

#include <boost/property_tree/json_parser.hpp>
#include <boost/property_tree/ptree.hpp>
using boost::property_tree::ptree;

struct service {
    std::string name;

    struct parameters_t {
        std::string para1, para2, para3;
    } parameters;
};

#include <boost/multi_index_container.hpp>
#include <boost/multi_index/ordered_index.hpp>
#include <boost/multi_index/member.hpp>

namespace bmi = boost::multi_index;

using Table = bmi::multi_index_container<
    service,
    bmi::indexed_by<
        bmi::ordered_unique<bmi::tag<struct by_name>,
            bmi::member<service, std::string, &service::name>
        >
    >
>;

#include <iostream>

Table read_json(std::string const& fname) {
    Table services;
    boost::property_tree::ptree pt;
    std::ifstream file(fname);
    boost::property_tree::read_json(file, pt);

    for (auto& v : pt.get_child("servicesList"))
    {
        auto& node = v.second;
        service svc;
        svc.name = node.get("serviceName", "");
        svc.parameters.para1 = node.get("serviceParameters.para1", "");
        svc.parameters.para2 = node.get("serviceParameters.para2", "");
        svc.parameters.para3 = node.get("serviceParameters.para3", "");

        if (!services.insert(svc).second)
            std::cout << "skipped duplicate service\n";
    }

    return services;
}

static inline std::ostream& operator<<(std::ostream& os, service const& s) {
    return os << "'" << s.name << "' params { "
        << "'" << s.parameters.para1 << "' "
        << "'" << s.parameters.para2 << "' "
        << "'" << s.parameters.para3 << "' }";
}

int main() {
    Table services = read_json("input.txt");

    for (auto& itr : services) {
        std::cout << itr.name << "\n";
    }

    auto it = services.find("ABC");
    assert(it != services.end());
    auto const& abc = *it;

    std::cout << abc << "\n";
}

打印

ABC
CBA
'ABC' params { 'value1' 'value2' 'value3' }