json-cpp 库使用

Json-cpp

         是一个使用c++开发的面向对象的json库。

核心数据结构

         Reader是json-cpp数据的读取器，可以从文件流，字符串中读取json数据，使用下面的接口：

         boolparse( const std::string &document,

                  Value &root,

                  bool collectComments = true);

         boolparse( std::istream &is,

                  Value &root,

                  bool collectComments = true);

         将所有的json解析到Value结果里面。

   Value是json解析的结果，它通过key-value的方式用来代表整数、浮点数、UTF-8的字符串、或者是一个value数组等，这个与json的格式定义保持一致。它的类型可以通过type获取，type的定义如下：

/*

* brief Type of the value held by a Value object.

   */

  enum ValueType

   {

     nullValue = 0, ///< ‘null‘ value

     intValue,      ///< signedinteger value

     uintValue,     ///< unsignedinteger value

     realValue,     ///< double value

     stringValue,   ///< UTF-8string value

     booleanValue,  ///< bool value

     arrayValue,    ///< array value(ordered list)

     objectValue    ///< objectvalue (collection of name/value pairs).

   };

   Value访问的常用接口：

      const char *asCString() const;

     std::string asString() const;

# ifdef JSON_USE_CPPTL

     CppTL::ConstString asConstString() const;

# endif

     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;

     bool isNull() const;

     bool isBool() const;

     bool isInt() const;

     bool isUInt() const;

     bool isIntegral() const;

     bool isDouble() const;

     bool isNumeric() const;

     bool isString() const;

     bool isArray() const;

     bool isObject() const;

     /// Return true if the object has a member named key.

     bool isMember( const char *key ) const;

     /// Return true if the object has a member named key.

     bool isMember( const std::string &key ) const;

# ifdef JSON_USE_CPPTL

     /// Return true if the object has a member named key.

     bool isMember( const CppTL::ConstString &key ) const;

# endif

     /// \brief Return a list of the member names.

     ///

     /// If null, return an empty list.

     /// \pre type() is objectValue or nullValue

     /// \post if type() was nullValue, it remains nullValue

     Members getMemberNames() const;

使用方法

#include "json/json.h"

#include "iostream"

#include "string"

int main()

{

   std::string strValue ="[{\"name\":\"TOM\",\"id\":4},{\"name\":\"JACK\",\"id\":5}]";

   Json::Reader reader;

   Json::Value value;

   if(reader.parse(strValue, value)) 

   {  

       if (value.type() != Json::arrayValue) {

           printf("Json type is not arrayValue %d\n", value.type());

           return 0;

       }  

       for(unsigned int i = 0;i < value.size(); i++)

       {  

            if (value[i].type() != Json::objectValue) {
                printf("Json type is not objectValue %d\n", value[i].type());
                continue;
            }          

            if(!value[i].isMember("name")) 

                continue;

           std::string name = value[i]["name"].asString(); 

           std::cout << "got name " << name <<std::endl;

           if(!value[i].isMember("id")) 

                continue;

           int id = value[i]["id"].asInt();

                                        std::cout << "got id" << id << std::endl;

           Json::Value::Members member = value[i].getMemberNames();

           for(Json::Value::Members::iterator iter = member.begin(); iter !=member.end(); ++iter)

           {

                std::cout << "gotmember " << (*iter) << std::endl;

           }

       }

    }

   return 0;

}

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