直接上码：

#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"
#include <sys/types.h>
#include <vector>

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


// 注意int和uint64_t
map<string,uint64_t> g_mChildInt;
map<string,string> g_mChildString;
string formJson(const map<string,int> &mInt,const map<string,string> &mString,const string &strChild="",uint64_t> &mChildInt=g_mChildInt,string> &mChildString=g_mChildString,const string &strChild2="",uint64_t> &mChildInt2=g_mChildInt,string> &mChildString2=g_mChildString)
{
	Document document;

    Document::AllocatorType& allocator = document.GetAllocator(); 
    Value root(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())
	{
		Value child(kObjectType);
		for(map<string,uint64_t>::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);
	}

	// 孩子级别
	if(!strChild2.empty())
	{
		Value child(kObjectType);
		for(map<string,uint64_t>::const_iterator it = mChildInt2.begin(); it != mChildInt2.end(); ++it) 
		{
			key.SetString(it->first.c_str(),string>::const_iterator it = mChildString2.begin(); it != mChildString2.end(); ++it)
		{
			key.SetString(it->first.c_str(),allocator);
		}

		key.SetString(strChild2.c_str(),allocator);
	}

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

}


string formJsonWithArray(const map<string,const string &strChild1,uint64_t> &mChildInt,string> &mChildString,string &strChild2,vector<map<string,uint64_t> >&mVecChildInt,string> >&mVecChildString)
		        
{
	Document document;
	
    Document::AllocatorType& allocator = document.GetAllocator(); 
    Value root(kObjectType);

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

	// 当前级别
	for(map<string,allocator);
	}

	// 孩子级别
	if(!strChild1.empty())
	{
		Value child(kObjectType);
		for(map<string,allocator);
		}

		key.SetString(strChild1.c_str(),allocator);
	}

	// 孩子级别
	unsigned int uiSize1 = mVecChildInt.size();
	unsigned int uiSize2 = mVecChildString.size();
	if(!strChild2.empty() && uiSize1 == uiSize2)
	{
		Value array(rapidjson::kArrayType);  
		for(unsigned int i = 0; i < uiSize1; ++i)
		{
			Value child(kObjectType);
			for(map<string,uint64_t>::iterator it = mVecChildInt[i].begin(); it != mVecChildInt[i].end(); ++it) 
			{
				key.SetString(it->first.c_str(),allocator);  
		    	child.AddMember(key,allocator);
	
			}
		
			for(map<string,string>::iterator it = mVecChildString[i].begin(); it != mVecChildString[i].end(); ++it)
			{
				key.SetString(it->first.c_str(),allocator);  
		   		value.SetString(it->second.c_str(),allocator);
			}

			array.PushBack(child,allocator);  

		}

		key.SetString(strChild2.c_str(),array,allocator);

	}

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


void test1()
{
	map<string,int> mInt;
	map<string,string> mString;
	mInt["code"] = 0;
	mString["msg"] = "ok";

	string strChild1 = "xxx";
	map<string,uint64_t> mChildInt1;
	map<string,string> mChildString1;
	mChildInt1["key"] = 729;
	mChildString1["kk"] = "vv";

	string strChild2 = "yyy";
	map<string,uint64_t> mChildInt2;
	map<string,string> mChildString2;
	mChildInt2["key"] = 730;
	mChildString2["kkk"] = "vvv";

	string s = formJson(mInt,mString,strChild1,mChildInt1,mChildString1,strChild2,mChildInt2,mChildString2);
	cout << s << endl;
}


void test2()
{
	map<string,uint64_t> mChildInt;
	map<string,string> mChildString;
	mChildString["kk"] = "vv";
	mChildInt["key"] = 729;


	string strChild2 = "data";
	vector<map<string,uint64_t> >mVecChildInt; 
	vector<map<string,string> >mVecChildString;

	{

		map<string,uint64_t> mChildInt; 
		map<string,string> mChildString;

		mChildInt["id"] = 1;
		mChildString["path"] = "pa";
		mChildString["sha"] = "sh";
			
		mVecChildInt.push_back(mChildInt);
		mVecChildString.push_back(mChildString);
	}

	{

		map<string,string> mChildString;

		mChildInt["id"] = 2;
		mChildString["path"] = "pa";
		mChildString["sha"] = "sh";
			
		mVecChildInt.push_back(mChildInt);
		mVecChildString.push_back(mChildString);
	}

	string s = formJsonWithArray(mInt,mChildInt,mChildString,mVecChildInt,mVecChildString);
	cout << s << endl;
}


int main(int argc,char *argv[])
{
	test1();
	test2();

	return 0;
}

{"code":0,"msg":"ok","xxx":{"key":729,"kk":"vv"},"yyy":{"key":730,"kkk":"vvv"}}
{"code":0,"data":[{"id":1,"path":"pa","sha":"sh"},{"id":2,"sha":"sh"}]}

不多说， 睡觉。