RapidJson开源库使用

1.下载

GitHub - Tencent/rapidjson: A fast JSON parser/generator for C++ with both SAX/DOM style APIA fast JSON parser/generator for C++ with both SAX/DOM style API - Tencent/rapidjsonhttps://github.com/Tencent/rapidjson

官方使用手册：RapidJSON: 首页（中文版）

2.RapidJson简介

RapidJSON特点：

（1）RapidJSON小而全：它同时支持SAX和DOM风格的API，SAX解析器只有约500行代码。

（2） RapidJSON快：它的性能可与strlen()相比，可支持SSE2/SSE4.2加速，使用模版及内联函数去降低函数调用开销。

（3）RapidJSON独立：它不依赖于BOOST等外部库，它甚至不依赖于STL。

（4）RapidJSON对内存友好：在大部分32/64位机器上，每个JSON值只占16字节(除字符串外)，它预设使用一个快速的内存分配器，令分析器可以紧凑地分配内存。

（5）RapidJSON对Unicode友好：它支持UTF-8、UTF-16、UTF-32(大端序/小端序)，并内部支持这些编码的检测、校验及转码。例如，RapidJSON可以在分析一个UTF-8文件至DOM (Document Object Model, 文件对象模型)时，把当中的JSON字符串转码至UTF-16。它也支持代理对(surrogate pair)及"\u0000"(空字符)。

每个JSON值都储存为Value类，而Document类则表示整个DOM，它存储了一个DOM 树的根Value。RapidJSON的所有公开类型及函数都在rapidjson命名空间中。

3.加载RapidJson库

在项目中只需要将 include/rapidjson 目录复制至系统或项目的 include 目录中。

4.代码示例

cpp 复制代码

#include "funset.hpp"
#include "rapidjson/document.h"
// #include "rapidjson/writer.h"
#include "rapidjson/prettywriter.h"
#include "rapidjson/stringbuffer.h"
#include <iostream>
#include <fstream>
#include <string>
#include "common.hpp"

int test_rapidjson_parse()
{
#ifdef _MSC_VER
    const char *file_name = "E:/GitCode/Messy_Test/testdata/json.data";
#else
    const char *file_name = "testdata/json.data";
#endif
    std::ifstream in(file_name);
    if (!in.is_open())
    {
        fprintf(stderr, "fail to read json file: %s\n", file_name);
        return -1;
    }

    std::string json_content((std::istreambuf_iterator<char>(in)), std::istreambuf_iterator<char>());
    in.close();

    rapidjson::Document dom;
    if (!dom.Parse(json_content.c_str()).HasParseError())
    {
        if (dom.HasMember("name") && dom["name"].IsString())
        {
            fprintf(stdout, "name: %s\n", dom["name"].GetString());
        }

        if (dom.HasMember("address") && dom["address"].IsString())
        {
            fprintf(stdout, "address: %s\n", utf8_to_gbk(dom["address"].GetString()));
        }

        if (dom.HasMember("age") && dom["age"].IsInt())
        {
            fprintf(stdout, "age: %d\n", dom["age"].GetInt());
        }

        const char *tmp = "xxx";
        if (!dom.HasMember(tmp))
        {
            fprintf(stdout, "Warning: it has no member: %s\n", tmp);
        }

        if (dom.HasMember("value1") && dom["value1"].IsArray())
        {
            const rapidjson::Value &arr = dom["value1"];
            for (int i = 0; i < arr.Size(); ++i)
            {
                const rapidjson::Value &tmp = arr[i];

                fprintf(stdout, "value1:\ni = %d:", i);
                for (int j = 0; j < tmp.Size(); ++j)
                {
                    if (tmp[j].IsInt())
                        fprintf(stdout, "%d, ", tmp[j].GetInt());
                    if (tmp[j].IsFloat())
                        fprintf(stdout, "%.1f, ", tmp[j].GetFloat());
                }
                fprintf(stdout, "\n");
            }
        }

        if (dom.HasMember("value2") && dom["value2"].IsArray())
        {
            const rapidjson::Value &arr = dom["value2"];

            fprintf(stdout, "value2: ");
            for (int i = 0; i < arr.Size(); ++i)
            {
                fprintf(stdout, "%.2f, ", arr[i].GetFloat());
            }
            fprintf(stdout, "\n");
        }

        if (dom.HasMember("bei_jing") && dom["bei_jing"].IsObject())
        {
            const rapidjson::Value &obj = dom["bei_jing"];

            if (obj.HasMember("address") && obj["address"].IsString())
            {
                fprintf(stdout, "address: %s\n", utf8_to_gbk(obj["address"].GetString()));
            }

            if (obj.HasMember("car") && obj["car"].IsBool())
            {
                fprintf(stdout, "car: %d\n", obj["car"].GetBool());
            }

            if (obj.HasMember("cat") && obj["cat"].IsBool())
            {
                fprintf(stdout, "cat: %d\n", obj["cat"].GetBool());
            }
        }

        if (dom.HasMember("shan_dong") && dom["shan_dong"].IsObject())
        {
            const rapidjson::Value &obj = dom["shan_dong"];

            if (obj.HasMember("address") && obj["address"].IsString())
            {
                fprintf(stdout, "address: %s\n", utf8_to_gbk(obj["address"].GetString()));
            }

            if (obj.HasMember("value1") && obj["value1"].IsArray())
            {
                const rapidjson::Value &arr = obj["value1"];

                if (arr[0].HasMember("ji_nan") && arr[0]["ji_nan"].IsString())
                {
                    fprintf(stdout, "ji_nan: %s\n", utf8_to_gbk(arr[0]["ji_nan"].GetString()));
                }

                if (arr[0].HasMember("tai_an") && arr[0]["tai_an"].IsString())
                {
                    fprintf(stdout, "tai_an: %s\n", utf8_to_gbk(arr[0]["tai_an"].GetString()));
                }
            }
        }
    }
    else
    {
        fprintf(stderr, "fail to parse json file: %s\n", file_name);
        return -1;
    }

    // iter json
    for (rapidjson::Value::ConstMemberIterator iter = dom.MemberBegin(); iter != dom.MemberEnd(); ++iter)
    {
        fprintf(stdout, "iter json name: %s, type: %d\n", iter->name.GetString(), iter->value.GetType());
    }

    return 0;
}

int test_rapidjson_write()
{
    rapidjson::StringBuffer buf;
    // rapidjson::Writer<rapidjson::StringBuffer> writer(buf);
    rapidjson::PrettyWriter<rapidjson::StringBuffer> writer(buf); // it can word wrap

    writer.StartObject();

    writer.Key("name");
    writer.String("spring");
    writer.Key("address");
    writer.String("北京");
    writer.Key("age");
    writer.Int(30);

    writer.Key("value1");
    writer.StartArray();
    writer.StartArray();
    writer.Double(23);
    writer.Double(43);
    writer.Double(-2.3);
    writer.Double(6.7);
    writer.Double(90);
    writer.EndArray();

    writer.StartArray();
    writer.Int(-9);
    writer.Int(-19);
    writer.Int(10);
    writer.Int(2);
    writer.EndArray();

    writer.StartArray();
    writer.Int(-5);
    writer.Int(-55);
    writer.EndArray();
    writer.EndArray();

    writer.Key("value2");
    writer.StartArray();
    writer.Double(13.3);
    writer.Double(1.9);
    writer.Double(2.10);
    writer.EndArray();

    writer.Key("bei_jing");
    writer.StartObject();
    writer.Key("address");
    writer.String("海淀");
    writer.Key("car");
    writer.Bool(false);
    writer.Key("cat");
    writer.Bool(true);
    writer.EndObject();

    writer.Key("shan_dong");
    writer.StartObject();
    writer.Key("address");
    writer.String("济南");
    writer.Key("value1");
    writer.StartArray();
    writer.Key("ji_nan");
    writer.String("趵突泉");
    writer.Key("tai_an");
    writer.String("泰山");
    writer.EndArray();
    writer.EndObject();

    writer.EndObject();

    const char *json_content = buf.GetString();
    fprintf(stdout, "json content: %s\n", json_content);

#ifdef _MSC_VER
    const char *file_name = "E:/GitCode/Messy_Test/testdata/out.json";
#else
    const char *file_name = "testdata/out.json";
#endif
    std::ofstream outfile;
    outfile.open(file_name);
    if (!outfile.is_open())
    {
        fprintf(stderr, "fail to open file to write: %s\n", file_name);
        return -1;
    }

    outfile << json_content << std::endl;
    outfile.close();

    return 0;
}

json文件内容如下所示：

cpp 复制代码

{
    "name": "spring",
    "address": "北京",
    "age": 30,
    "value1": [
        [
            23,
            43,
            -2.3,
            6.7,
            90
        ],
        [
            -9,
            -19,
            10,
            2
        ],
        [
            -5,
            -55
        ]
    ],
    "value2": [
        13.3,
        1.9,
        2.10
    ],
    "bei_jing": {
        "address": "海淀",
        "car": false,
        "cat": true
    },
    "shan_dong": {
        "address": "济南",
        "value1": [
            {
                "ji_nan": "趵突泉"
            },
            {
                "tai_an": "泰山"
            }
        ]
    }
}