看代码：

#include <iostream>
#include <map>

// 请自己下载开源的rapidjson
#include "rapidjson/prettywriter.h"
#include "rapidjson/rapidjson.h"
#include "rapidjson/document.h"
#include "rapidjson/stringbuffer.h"
#include "rapidjson/writer.h"
#include "rapidjson/memorystream.h"

using namespace std;
using rapidjson::Document;
using rapidjson::StringBuffer;
using rapidjson::Writer;
using namespace rapidjson;


string formJson(const map<string,int> &mInt,const map<string,string> &mString,const string &strChild,int> &mChildInt,string> &mChildString)
{
	Document document;

    Document::AllocatorType& allocator = document.GetAllocator(); 
    Value root(kObjectType);
	Value child(kObjectType);

    Value key(kStringType);  
    Value value(kStringType); 

	// 当前级别
	for(map<string,int>::const_iterator it = mInt.begin(); it != mInt.end(); ++it) 
	{
		key.SetString(it->first.c_str(),allocator);  
    	root.AddMember(key,it->second,allocator);
	}

	for(map<string,string>::const_iterator it = mString.begin(); it != mString.end(); ++it)
	{
		key.SetString(it->first.c_str(),allocator);  
   		value.SetString(it->second.c_str(),value,allocator);
	}


	// 孩子级别
	if(!strChild.empty())
	{
		for(map<string,int>::const_iterator it = mChildInt.begin(); it != mChildInt.end(); ++it) 
		{
			key.SetString(it->first.c_str(),allocator);  
	    	child.AddMember(key,allocator);
		}

		for(map<string,string>::const_iterator it = mChildString.begin(); it != mChildString.end(); ++it)
		{
			key.SetString(it->first.c_str(),allocator);  
	   		value.SetString(it->second.c_str(),allocator);
		}

		key.SetString(strChild.c_str(),allocator); 
		root.AddMember(key,child,allocator);
	}


    StringBuffer buffer;  
    Writer<StringBuffer> writer(buffer);  
    root.Accept(writer);  
    return buffer.GetString();  

}


int main(int argc,char *argv[])
{
	map<string,int> mInt;
	mInt["code"] = 0;
	mInt["score"] = 80;

	map<string,string> mString;
	mString["name"] = "taoge";
	mString["place"] = "shenzhen";


	string strChild = "childNode";

	map<string,int> mChildInt;
	mChildInt["code"] = 0;
	mChildInt["score"] = 100;

	map<string,string> mChildString;
	mChildString["name"] = "taogeChild";
	mChildString["place"] = "shenzhen";

	
	string strJson = formJson(mInt,mString,strChild,mChildInt,mChildString);
	cout << strJson << endl;
	return 0;
}

{"code":0,"score":80,"name":"taoge","place":"shenzhen","childNode":{"code":0,"score":100,"name":"taogeChild","place":"shenzhen"}}

另外， 如果仅仅想有当前界别， 那么， 可以这么搞（C++默认参数搞起）：

#include <iostream>
#include <map>

// 请自己下载开源的rapidjson
#include "rapidjson/prettywriter.h"
#include "rapidjson/rapidjson.h"
#include "rapidjson/document.h"
#include "rapidjson/stringbuffer.h"
#include "rapidjson/writer.h"
#include "rapidjson/memorystream.h"

using namespace std;
using rapidjson::Document;
using rapidjson::StringBuffer;
using rapidjson::Writer;
using namespace rapidjson;


map<string,int> g_mChildInt;
map<string,string> g_mChildString;


string formJson(const map<string,const string &strChild="",int> &mChildInt=g_mChildInt,string> &mChildString=g_mChildString)
{
	Document document;

    Document::AllocatorType& allocator = document.GetAllocator(); 
    Value root(kObjectType);
	Value child(kObjectType);

    Value key(kStringType);  
    Value value(kStringType); 

	// 当前级别
	for(map<string,string> mString;
	mString["name"] = "taoge";
	mString["place"] = "shenzhen";

	
	string strJson = formJson(mInt,mString);
	cout << strJson << endl;
	return 0;
}

{"code":0,"place":"shenzhen"}

其实， 上面的formJson函数， 还可以继续扩展。