RapidJSON简介及使用

素颜马尾好姑娘i 2022-01-21 03:09 537阅读 0赞

RapidJSON是腾讯开源的一个高效的C++ JSON解析器及生成器，它是只有头文件的C++库。RapidJSON是跨平台的，支持Windows, Linux, Mac OS X及iOS, Android。它的源码在[https://github.com/Tencent/rapidjson/][https_github.com_Tencent_rapidjson]，稳定版本为2016年发布的1.1.0版本。

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。

以上内容摘自：[http://rapidjson.org/zh-cn/][http_rapidjson.org_zh-cn]，关于RapidJSON的更详细介绍可以参考此网页。

以下是测试代码(test\_rapidjson.cpp)：

#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.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.data内容如下：

{
      "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"}]
      }
    }

test\_rapidjson\_parse的执行结果如下：与实际结果一致

![watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L2ZlbmdiaW5nY2h1bg_size_16_color_FFFFFF_t_70][]

test\_rapidjson\_write的执行结果如下：与预期一致，将rapidjson::Writer<rapidjson::StringBuffer> writer(buf)调整为rapidjson::PrettyWriter<rapidjson::StringBuffer> writer(buf);可使结果自动换行

![20190607205243648.png][]

**GitHub**：[https://github.com/fengbingchun/Messy\_Test][https_github.com_fengbingchun_Messy_Test]

[https_github.com_Tencent_rapidjson]: https://github.com/Tencent/rapidjson/
[http_rapidjson.org_zh-cn]: http://rapidjson.org/zh-cn/
[watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L2ZlbmdiaW5nY2h1bg_size_16_color_FFFFFF_t_70]: /images/20220121/38509ae4101249b3b2a3afdd92700223.png
[20190607205243648.png]: /images/20220121/f085d41f4e27476ea4b8ba2f6e45f126.png
[https_github.com_fengbingchun_Messy_Test]: https://github.com/fengbingchun/Messy_Test