需求：
在对mongodb中的字段值进行解析的时候发现，因为这个值是json字符串，需要对其进行反序列化。
解决方法：
首先想到了到http://www.json.org/json-zh.html网站去找相应的C++库，试了一下jsoncpp和JSON Spirit，因为是用scons来构建了，装了一下，编译以后玩不起来，放弃了。再试JSON Spirit，(http://www.codeproject.com/Articles/20027/JSON-Spirit-A-C-JSON-Parser-Generator-Implemented)， 这东东不错，好像是依赖于Boost Spirit的，这个我也装了，安装过程还是满方便的，因为我的C++项目都是用CMake的，这个也是用它的，所以编译安装没有遇到什么问题。下面给出一个相应的例子：
- #include <json_spirit.h>
-
- const std::string test =
- "{"
- " \"text\": \"Home-plate umpire Crawford gets stung http://tinyurl.com/27ujc86\","
- " \"favorited\": false,"
- " \"source\": \"<a href=\\\"http://apiwiki.twitter.com/\\\" rel=\\\"nofollow\\\">API</a>\","
- " \"user\": {"
- " \"name\": \"Johnathan Thomas\""
- " }"
- "}";
-
-
- int main() {
- namespace js = json_spirit;
- js::mValue top;
- js::read(std::string(test), top);
- json_spirit::mObject obj = top.get_obj();
- std::cout << "--------" << std::endl;
-
- std::cout
- << obj["text" ].get_str() << "\n"
- << obj["favorited"].get_bool() << "\n"
- << obj["source" ].get_str() << "\n"
- << obj["user" ].get_obj()["name"].get_str() << "\n";
- }
下面想到了mongodb有自己的bson结构，这个东东和json是差不多的，在mongodb的源代码包里找到了json.h这个文件看，盾到了fromjson这个方法，看来能行。呵呵
下面是我的测试代码，因为我的value中用到了array，这里还用到了别外一个把BSONObj转换成Array<BSONObj>的方法。
- #include <db/json.h> // load fromjson method
-
- #include <iostream>
- #include <string>
- const std::string test =
- "{ \"specs\" : "
- " [ {\"id\":\"value1\" , \"name\":\"jack\"},"
- " {\"id\": \"value2\", \"name\":\"jack2\"},"
- "{\"id\": \"value3\", \"name\":\"jack3\"}"
- " ]"
- "}";
-
-
- int main()
- {
- try{
- // { "specs" : [ {"id":"value1" , "name":"jack"}, {"id": "value2", "name":"jack2"},{"id": "value3", "name":"jack3"} ]}
- std::cout << "Test json string:" << test << std::endl;
-
-
- // parse json method from json.h file
- // throws MsgAssertionException if parsing fails. The message included with
- // this assertion includes a rough indication of where parsing failed.
- mongo::BSONObj obj = mongo::fromjson(test);
- mongo::BSONObj eles = obj["specs"].Obj(); // get array obj
-
-
- /** add all values of the object to the specified vector. If type mismatches, exception.
- this is most useful when the BSONObj is an array, but can be used with non-arrays too in theory.
-
-
- example:
- bo sub = y["subobj"].Obj();
- vector<int> myints;
- sub.Vals(myints);
- */
-
-
- vector<mongo::BSONObj> specs;
- eles.Vals(specs);
-
-
- // print values
- for(int i = 0; i < 3; ++i)
- std::cout << specs.at(i)["id"].String() << ":" << specs.at(i)["name"].String()<< endl;
- }
- catch(const mongo::MsgAssertionException& e)
- {
- std::cout << "parse exception " << e.what() << endl;
- }
- }
运行结果：
- gxl@gxl-desktop:~/Test_place$ g++ sample.cpp -o sample -I/usr/local/include/mongo/ -lmongoclient
- gxl@gxl-desktop:~/Test_place$ ./sample
- Test json string:{ "specs" : [ {"id":"value1" , "name":"jack"}, {"id": "value2", "name":"jack2"},{"id": "value3", "name":"jack3"} ]}
- value1:jack
- value2:jack2
- value3:jack3
分类：
