【C++】Boost库之Json工具

目前的Boost库为1.80，其中的Json工具使用示例如下：

//
//  main.cpp
//
//  Created by Tao on 2022/11/27.
//

#include 
#include 
#include 

namespace json = boost::json;

json::value parse_demo_str(std::string str) {
    json::stream_parser p;
    json::error_code ec;
    
    p.write(str.c_str(), str.length(), ec);
    if( ec )
        return nullptr;
    
    p.finish( ec );
    if( ec )
        return nullptr;
    return p.release();
}

void pretty_print( std::ostream& os, json::value const& jv, std::string* indent = nullptr ) {
    std::string indent_;
    if(! indent)
        indent = &indent_;
    
    switch(jv.kind())
    {
        case json::kind::object:
        {
            os << "{\n";
            indent->append(4, ' ');
            auto const& obj = jv.get_object();
            if(! obj.empty())
            {
                auto it = obj.begin();
                for(;;)
                {
                    os << *indent << json::serialize(it->key()) << " : ";
                    pretty_print(os, it->value(), indent);
                    if(++it == obj.end())
                        break;
                    os << ",\n";
                }
            }
            os << "\n";
            indent->resize(indent->size() - 4);
            os << *indent << "}";
            break;
        }
            
        case json::kind::array:
        {
            os << "[\n";
            indent->append(4, ' ');
            auto const& arr = jv.get_array();
            if(! arr.empty())
            {
                auto it = arr.begin();
                for(;;)
                {
                    os << *indent;
                    pretty_print( os, *it, indent);
                    if(++it == arr.end())
                        break;
                    os << ",\n";
                }
            }
            os << "\n";
            indent->resize(indent->size() - 4);
            os << *indent << "]";
            break;
        }
            
        case json::kind::string:
        {
            os << json::serialize(jv.get_string());
            break;
        }
            
        case json::kind::uint64:
            os << jv.get_uint64();
            break;
            
        case json::kind::int64:
            os << jv.get_int64();
            break;
            
        case json::kind::double_:
            os << jv.get_double();
            break;
            
        case json::kind::bool_:
            if(jv.get_bool())
                os << "true";
            else
                os << "false";
            break;
            
        case json::kind::null:
            os << "null";
            break;
    }
    
    if(indent->empty())
        os << "\n";
}

int main(int argc, char** argv) {
    std::string str = R"+({
    "pi": 3.141,
    "happy": true,
    "name": "Boost",
    "nothing": null,
    "answer": {
      "everything": 42
    },
    "list": [1, 0, 2],
    "object": {
      "currency": "USD",
      "value": 42.99
    }
    })+";
    
    try {
        // Parse the string as JSON
        auto const jv = parse_demo_str(str);
        
        // Now pretty-print the value
        pretty_print(std::cout, jv);
    } catch (std::exception const& e) {
        std::cerr << "Caught exception: " << e.what() << std::endl;
        return EXIT_FAILURE;
    }
    
    return EXIT_SUCCESS;
}

使用解析器可以将一段字符串（模拟报文）解析为一个通用json value对象，再通过该对象来进行取值并进行打印查看。更多示例见后续更新。