C++ write big files (10G+) continuously,pour data into the file and release memory manually

#pragma comment(lib,"rpcrt4.lib")
#include<Windows.h>
#include<iostream>
#include<algorithm>
#include<string>
#include<fstream>
#include<ostream>
#include<istream>
#include<sstream>

using namespace std; 

void logFileDemo2();
void getUuid(string& str); 

int main()
{
    logFileDemo2();
    getchar();
}
 
void logFileDemo2()
{
    string logFileName = "logFile.txt";
    fstream logFile(logFileName, ios::app);
    unsigned long long num = 0;
    while (1)
    {
        if (GetAsyncKeyState(VK_ESCAPE))
        {
            cout << "Stop!";
            break;
        }

        stringstream ss;
        string str="";
        for (int i = 0; i < 1000000; i++)
        {
            getUuid(str);
            ss << ++num << "," << str << endl; 
            str = std::string();
        }
        logFile << ss.str() << endl;
        ss = std::stringstream();
        cout << num << endl; 
    }

    logFile.close();
    cout << "Finished!" << endl; 
}

 
void getUuid(string &str)
{
    UUID newUUID;
    UuidCreate(&newUUID); 
    char* str2;
    UuidToStringA(&newUUID, (RPC_CSTR*)&str2);
    str = str2;
    RpcStringFreeA((RPC_CSTR*)&str2);
}

C++ has no GC concept,the programmer must release memory manually. So that this will avoid out of memory ,memory leak.