一、jsoncpp库概述
库的安装
sudo apt-get install libjsoncpp-dev
- 安装完成之后,头文件默认安装在/usr/include/jsoncpp/json/目录下,库API文档默认在/usr/share/doc/libjsoncpp-dev/目录下
编译带有jsoncpp库的C++程序
- 使用如下的命令进行编译,编译时带上-ljsoncpp选项即可
- 例如:
g++ jsoncpp_demo01.c -o demo01 -ljsoncpp -std=c++11
二、jsoncpp支持的值
- jsoncpp 使用 Json::Value 对象来保存 JSON 串,Json::Value 对象可以表示如下数据类 型:
三、相关接口
检测保存的数据类型
bool isNull() const;
bool isBool() const;
bool isInt() const;
bool isInt64() const;
bool isUInt() const;
bool isUInt64() const;
bool isIntegral() const;
bool isDouble() const;
bool isNumeric() const;
bool isString() const;
bool isArray() const;
bool isObject() const;
基础数据类型的访问
const char* asCString() const;
JSONCPP_STRING asString() const;
Int asInt() const;
UInt asUInt() const;
Int64 asInt64() const;
UInt64 asUInt64() const;
LargestInt asLargestInt() const;
LargestUInt asLargestUInt() const;
float asFloat() const;
double asDouble() const;
bool asBool() const;
数组风格
- ValueType::arrayValue 和 ValueType::objectValue 数据类型的访问,操作方式很类似 C++的 vector,可以使用数组风格或者迭代器风格来操作数据。例如:
root["name"] = "milo";
ArrayIndex size() const;
Value& operator[](ArrayIndex index);
Value& operator[](int index);
const Value& operator[](ArrayIndex index) const;
const Value& operator[](int index) const;
Value get(ArrayIndex index, const Value& defaultValue) const;
const_iterator begin() const;
const_iterator end() const;
iterator begin();
iterator end();
- ValueType::objectValue 数据类型的访问,操作方式很类似 C++的 map
Value& operator[](const char* key);
const Value& operator[](const char* key) const;
Value& operator[](const JSONCPP_STRING& key);
const Value& operator[](const JSONCPP_STRING& key) const;
Value& operator[](const StaticString& key);
Value& operator[](const CppTL::ConstString& key);
const Value& operator[](const CppTL::ConstString& key) const;
Value get(const char* key, const Value& defaultValue) const;
Value get(const char* begin, const char* end, const Value& defaultValue) const;
Value get(const JSONCPP_STRING& key, const Value& defaultValue) const;
Value get(const CppTL::ConstString& key, const Value& defaultValue) const;
修改数据
- 知道如何获取 Json::Value 对象或其子对象后,我们来看下如何修改 Json::Value 保存 的数据:
- 直接使用=赋值就可以了
Value& operator=(Value other);
- 因为 Json::Value 已经实现了各种数据类型的构造函数
Value(ValueType type = nullValue);
Value(Int value);
Value(UInt value);
Value(Int64 value);
Value(UInt64 value);
Value(double value);
Value(const char* value);
Value(const char* begin, const char* end);
Value(const StaticString& value);
Value(const JSONCPP_STRING& value);
Value(const CppTL::ConstString& value);
Value(bool value);
Value(const Value& other);
Value(Value&& other);
四、注意事项
类型转换
- 对于Int、Uint、Int64、UInt64等类型,注意类型。
root["age"] = 80; //默认为Int类型
root["age"] = (Json::Uint)80;
空值
root["address"] = Json::nullValue;
五、演示案例1
代码如下
#include <iostream>
#include <string>
#include <jsoncpp/json/json.h>
int main()
{
std::cout << "Hello World!" << std::endl;
Json::Value root;
Json::FastWriter fast;
root["ModuleType"] = Json::Value(1);
root["ModuleCode"] = Json::Value("China");
std::cout<<fast.write(root)<<std::endl;
Json::Value sub;
sub["version"] = Json::Value("1.0");
sub["city"] = Json::Value(root);
fast.write(sub);
std::cout<<sub.toStyledString()<<std::endl;
return 0;
}
g++ jsoncpp_demo01.c -o demo01 -ljsoncpp -std=c++11
六、演示案例2
代码如下
#include <string>
#include <jsoncpp/json/json.h>
#include <iostream>
using namespace std;
void readJson() {
std::string strValue = "{\"name\":\"json\",\"array\":[{\"cpp\":\"jsoncpp\"},{\"java\":\"jsoninjava\"},{\"php\":\"support\"}]}";
Json::Reader reader;
Json::Value value;
if (reader.parse(strValue, value))
{
std::string out = value["name"].asString();
std::cout << out << std::endl;
const Json::Value arrayObj = value["array"];
for (unsigned int i = 0; i < arrayObj.size(); i++)
{
if (!arrayObj[i].isMember("cpp"))
continue;
out = arrayObj[i]["cpp"].asString();
std::cout << out;
if (i != (arrayObj.size() - 1))
std::cout << std::endl;
}
}
}
void writeJson() {
Json::Value root;
Json::Value arrayObj;
Json::Value item;
item["cpp"] = "jsoncpp";
item["java"] = "jsoninjava";
item["php"] = "support";
arrayObj.append(item);
root["name"] = "json";
root["array"] = arrayObj;
root.toStyledString();
std::string out = root.toStyledString();
std::cout << out << std::endl;
}
int main(int argc, char** argv) {
readJson();
writeJson();
return 0;
}
g++ jsoncpp_demo02.c -o demo02 -ljsoncpp -std=c++11
七、演示案例3
代码如下
//测试jsoncpp的使用方法和性能
#include <memory>
#include <sstream>
#include <iostream>
#include <stdint.h>
#include <unistd.h>
#include <sys/time.h>
#include <sys/wait.h>
#include "jsoncpp/json/json.h"
#include "jsoncpp/json/value.h"
#include "jsoncpp/json/reader.h"
#include "jsoncpp/json/writer.h"
/*
{
"name": "milo",
"age": 80,
"languages": ["C++", "C"],
"phone": {
"number": "186****3143",
"type": "home"
},
"books":[
{
"name": "Linux kernel development",
"price":7.7
},
{
"name": "Linux server development",
"price": 8.0
}
],
"vip":true,
"address": null
}
*/
static uint64_t getNowTime()
{
struct timeval tval;
uint64_t nowTime;
gettimeofday(&tval, NULL);
nowTime = tval.tv_sec * 1000L + tval.tv_usec / 1000L;
return nowTime;
}
std::string JsoncppEncodeNew()
{
std::string jsonStr;
// 一个value是可以包含多个键值对
Json::Value root, languages, phone, book, books;
// 姓名
root["name"] = "milo";
// 年龄
root["age"] = 80;
// 语言
languages[0] = "C++";
languages[1] = "Java";
root["languages"] = languages;
// 电话
phone["number"] = "186****3143";
phone["type"] = "home";
root["phone"] = phone;
// 书籍
book["name"] = "Linux kernel development";
book["price"] = 7.7;
books[0] = book; // 深拷贝
book["name"] = "Linux server development";
book["price"] = 8.0;
books[1] = book; // 深拷贝
root["books"] = books;
// 是否为vip
root["vip"] = true;
// address信息空null
root["address"] = "yageguoji";
Json::StreamWriterBuilder writerBuilder;
std::ostringstream os;
std::unique_ptr<Json::StreamWriter> jsonWriter(writerBuilder.newStreamWriter());
jsonWriter->write(root, &os);
jsonStr = os.str();
// std::cout << "Json:\n" << jsonStr << std::endl;
return jsonStr;
}
std::string JsoncppEncodeOld()
{
std::string jsonStr;
Json::Value root, languages, phone, book, books;
// 姓名
root["name"] = "milo";
//root["name"] = Json::nullValue;
// 年龄
root["age"] = 80;
// 语言
languages[0] = "C++";
languages[1] = "Java";
root["languages"] = languages;
// 电话
phone["number"] = "186****3143";
phone["type"] = "home";
root["phone"] = phone;
// 书籍
book["name"] = "Linux kernel development";
book["price"] = (float)7.7;
books[0] = book;
book["name"] = "Linux server development";
book["price"] = (float)8.0;
books[1] = book;
root["books"] = books;
// 是否为vip
root["vip"] = true;
// address信息空null
root["address"] = "yageguoji"; //;// Json::nullValue; // 如果是null,则要用自定义的Json::nullValue,不能用NULL
Json::FastWriter writer;
jsonStr = writer.write(root);
// std::cout << "Json:\n" << jsonStr << std::endl;
return jsonStr;
}
// 不能返回引用
Json::Value JsoncppEncodeOldGet()
{
Json::Value root;
Json::Value languages, phone, book, books;
// 姓名
root["name"] = "milo";
//root["name"] = Json::nullValue;
// 年龄
root["age"] = 80;
// 语言
languages[0] = "C++";
languages[1] = "Java";
root["languages"] = languages;
// 电话
phone["number"] = "186****3143";
phone["type"] = "home";
root["phone"] = phone;
// 书籍
book["name"] = "Linux kernel development";
book["price"] = (float)7.7;
books[0] = book;
book["name"] = "Linux server development";
book["price"] = (float)8.0;
books[1] = book;
root["books"] = books;
// 是否为vip
root["vip"] = true;
// address信息空null
root["address"] = Json::nullValue; //"yageguoji";// Json::nullValue; // 如果是null,则要用自定义的Json::nullValue,不能用NULL
std::cout << "JsoncppEncodeOldGet:\n" << std::endl;
return root;
}
void printJsoncpp(Json::Value &root)
{
if(root["name"].isNull())
{
std::cout << "name null\n";
}
std::cout << "name: " << root["name"].asString() << std::endl;
std::cout << "age: " << root["age"].asInt() << std::endl;
Json::Value &languages = root["languages"];
std::cout << "languages: ";
for (uint32_t i = 0; i < languages.size(); ++i)
{
if (i != 0)
{
std::cout << ", ";
}
std::cout << languages[i].asString();
}
std::cout << std::endl;
Json::Value &phone = root["phone"];
std::cout << "phone number: " << phone["number"].asString() << ", type: " << phone["type"].asString() << std::endl;
Json::Value &books = root["books"];
for (uint32_t i = 0; i < books.size(); ++i)
{
Json::Value &book = books[i];
std::cout << "book name: " << book["name"].asString() << ", price: " << book["price"].asFloat() << std::endl;
}
std::cout << "vip: " << root["vip"].asBool() << std::endl;
if (!root["address"].isNull())
{
std::cout << "address: " << root["address"].asString() << std::endl;
}
else
{
std::cout << "address is null" << std::endl;
}
}
bool JsoncppDecodeNew(const std::string &info)
{
if (info.empty())
return false;
bool res;
JSONCPP_STRING errs;
Json::Value root;
Json::CharReaderBuilder readerBuilder;
std::unique_ptr<Json::CharReader> const jsonReader(readerBuilder.newCharReader());
res = jsonReader->parse(info.c_str(), info.c_str() + info.length(), &root, &errs);
if (!res || !errs.empty())
{
std::cout << "parseJson err. " << errs << std::endl;
return false;
}
// printJsoncpp(root);
return true;
}
bool JsoncppDecodeOld(const std::string &strJson)
{
if (strJson.empty())
return false;
bool res;
Json::Value root;
Json::Reader jsonReader;
res = jsonReader.parse(strJson, root);
if (!res)
{
std::cout << "jsonReader.parse err. " << std::endl;
return false;
}
// printJsoncpp(root);
return true;
}
const char *strCjson = "{ \
\"name\": \"milo\", \
\"age\": 80, \
\"languages\": [\"C++\", \"C\"],\
\"phone\": { \
\"number\": \"186****3143\", \
\"type\": \"home\" \
}, \
\"books\": [{ \
\"name\": \"Linux kernel development\", \
\"price\": 7.700000 \
}, { \
\"name\": \"Linux server development\", \
\"price\": 8 \
}], \
\"vip\": true, \
\"address\": null \
} \
";
#define TEST_COUNT 100000
int main()
{
std::string jsonStrNew;
std::string jsonStrOld;
jsonStrNew = JsoncppEncodeNew();
// JsoncppEncodeNew size: 337
std::cout << "JsoncppEncodeNew size: " << jsonStrNew.size() << std::endl;
std::cout << "JsoncppEncodeNew string: " << jsonStrNew << std::endl;
JsoncppDecodeNew(jsonStrNew);
jsonStrOld = JsoncppEncodeOld();
// JsoncppEncodeOld size: 248
std::cout << "\n\nJsoncppEncodeOld size: " << jsonStrOld.size() << std::endl;
std::cout << "JsoncppEncodeOld string: " << jsonStrOld << std::endl;
JsoncppDecodeOld(jsonStrOld);
Json::Value root = JsoncppEncodeOldGet();
Json::FastWriter writer;
std::cout << "writer:\n" << std::endl;
std::string jsonStr = writer.write(root);
std::cout << "\n\njsonStr string: " << jsonStrOld << std::endl;
#if 1
uint64_t startTime;
uint64_t nowTime;
startTime = getNowTime();
std::cout << "jsoncpp encode time testing" << std::endl;
for(int i = 0; i < TEST_COUNT; i++)
{
JsoncppEncodeNew();
}
nowTime = getNowTime();
std::cout << "jsoncpp encode " << TEST_COUNT << " time, need time: "
<< nowTime-startTime << "ms" << std::endl;
startTime = getNowTime();
std::cout << "\njsoncpp encode time testing" << std::endl;
for(int i = 0; i < TEST_COUNT; i++)
{
JsoncppEncodeOld();
}
nowTime = getNowTime();
std::cout << "jsoncpp encode " << TEST_COUNT << " time, need time: "
<< nowTime-startTime << "ms" << std::endl;
startTime = getNowTime();
std::cout << "\njsoncpp decode time testing" << std::endl;
for(int i = 0; i < TEST_COUNT; i++)
{
JsoncppDecodeNew(jsonStrNew);
}
nowTime = getNowTime();
std::cout << "jsoncpp decode " << TEST_COUNT << " time, need time: "
<< nowTime-startTime << "ms" << std::endl;
startTime = getNowTime();
std::cout << "\njsoncpp decode time testing" << std::endl;
for(int i = 0; i < TEST_COUNT; i++)
{
JsoncppDecodeOld(jsonStrNew);
}
nowTime = getNowTime();
std::cout << "jsoncpp decode " << TEST_COUNT << " time, need time: "
<< nowTime-startTime << "ms" << std::endl;
#endif
return 0;
}
g++ jsoncpp_speed.cpp -o jsoncpp_speed -ljsoncpp -std=c++11