因项目需求，需要使用 C++ 解析 JSON。
RapidJSON
第一种方法，使用 RapidJSON 可以方便的用来生成或者解析 JSON。
项目地址：https://github.com/miloyip/rapidjson
RapidJSON 是只有头文件的 C++ 库。使用时只需要把 include/rapidjson 复制到项目目录中即可。
类似如下的JSON，其中包括Object，包括Array，掌握解析该JSON，基本 RapidJSON 解析可掌握：
{
"ret": "101",
"error": [
{
"errortype": "A0001",
"errorstroke": {
"0": "0.2",
"1": "0.3"
}
},
{
"errortype": "A0021",
"errorstroke": {
"0": "0.2",
"1": "0.3"
}
}
]
}
代码如下：
#include <iostream>
#include <vector>
#include <string>
#include "rapidjson/document.h"
#include "rapidjson/writer.h"
#include "rapidjson/stringbuffer.h"
using namespace rapidjson;
using namespace std;
int main() {
string ret =
"{\"ret\":\"101\",\"error\":[{\"errortype\":\"A0001\",\"errorstroke\":{\"0\":\"0.2\",\"1\":\"0.3\"}},{\"errortype\":\"A0021\",\"errorstroke\":{\"0\":\"0.2\",\"1\":\"0.3\"}}]}";
rapidjson::Document doc;
doc.Parse<kParseDefaultFlags>(ret.c_str());
if (doc.HasMember("ret")) {
string retjson = doc["ret"].GetString();
for (unsigned i = 0; i < retjson.length(); ++i) {
cout << retjson.at(i) << " ";
}
}
cout << endl;
if (doc.HasMember("error")) {
const Value & errorjson = doc["error"];
for (SizeType i = 0; i < errorjson.Size(); ++i) {
// 或者这里可以换用一种遍历使用 Value::ConstValueIterator
// http://rapidjson.org/md_doc_tutorial.html#QueryArray
if (errorjson[i].HasMember("errortype")) {
string errortype = errorjson[i]["errortype"].GetString();
cout << "errortype: " << errortype << endl;
}
if (errorjson[i].HasMember("errorstroke")) {
const Value & errorstroke = errorjson[i]["errorstroke"];
cout << "errorstroke" << endl;
for (Value::ConstMemberIterator iter = errorstroke.MemberBegin();iter != errorstroke.MemberEnd(); ++iter) {
cout << iter->name.GetString() << ": " << iter->value.GetString() << endl;
}
}
}
}
return 0;
}
关于 RapidJSON 的更多内容可以参考官网。
boost property_tree
使用 boost 库中的 property_tree 解析如下：
/*
first config your project to include /usr/local/include
second link lib /usr/local/lib
*/
#include <iostream>
#include <boost/property_tree/ptree.hpp>
#include <boost/property_tree/json_parser.hpp>
#include <boost/foreach.hpp>
#include <string>
using namespace boost::property_tree;
int main(int argc, const char * argv[]) {
std::string str_json = "{\"ret\":\"101\",\"error\":[{\"errortype\":\"A0001\",\"errorstroke\":{\"0\":\"0.2\",\"1\":\"0.3\"}},{\"errortype\":\"A0021\",\"errorstroke\":{\"0\":\"0.2\",\"1\":\"0.3\"}}]}";
ptree pt; //define property_tree object
std::stringstream ss(str_json);
try {
read_json(ss, pt); //parse json
} catch (ptree_error & e) {
return 1;
}
std::cout << pt.get<std::string>("ret") << std::endl;
ptree errortype = pt.get_child("error"); // get_child to get errors
// first way
for (boost::property_tree::ptree::iterator it = errortype.begin(); it != errortype.end(); ++it) {
std::cout << it->first;
std::cout << it->second.get<std::string>("errortype") << std::endl;
ptree errorstroke = it->second.get_child("errorstroke");
for (ptree::iterator iter = errorstroke.begin(); iter != errorstroke.end(); ++iter) {
std::string key = iter->first;
std::cout << iter->first << std::endl;
std::cout << iter->second.data() << std::endl;
}
}
// second way: using boost foreach feature
// BOOST_FOREACH(ptree::value_type &v, errortype){
// ptree& childparse = v.second;
// std::cout << childparse.get<std::string>("errortype") << std::endl;
// ptree errorstroke = childparse.get_child("errorstroke");
// BOOST_FOREACH(ptree::value_type& w, errorstroke){
// std::cout << w.first << std::endl;
// std::cout << w.second.data() << std::endl;
// }
// }
/*
101
A0001
0
0.2
1
0.3
A0021
0
0.2
1
0.3
*/
return 0;
}