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

 1 #pragma comment(lib,"rpcrt4.lib")
 2 #include<Windows.h>
 3 #include<iostream>
 4 #include<algorithm>
 5 #include<string>
 6 #include<fstream>
 7 #include<ostream>
 8 #include<istream>
 9 #include<sstream>
10 
11 using namespace std; 
12 
13 void logFileDemo2();
14 void getUuid(string& str); 
15 
16 int main()
17 {
18     logFileDemo2();
19     getchar();
20 }
21  
22 void logFileDemo2()
23 {
24     string logFileName = "logFile.txt";
25     fstream logFile(logFileName, ios::app);
26     unsigned long long num = 0;
27     while (1)
28     {
29         if (GetAsyncKeyState(VK_ESCAPE))
30         {
31             cout << "Stop!";
32             break;
33         }
34 
35         stringstream ss;
36         string str="";
37         for (int i = 0; i < 1000000; i++)
38         {
39             getUuid(str);
40             ss << ++num << "," << str << endl; 
41             str = std::string();
42         }
43         logFile << ss.str() << endl;
44         ss = std::stringstream();
45         cout << num << endl; 
46     }
47 
48     logFile.close();
49     cout << "Finished!" << endl; 
50 }
51 
52  
53 void getUuid(string &str)
54 {
55     UUID newUUID;
56     UuidCreate(&newUUID); 
57     char* str2;
58     UuidToStringA(&newUUID, (RPC_CSTR*)&str2);
59     str = str2;
60     RpcStringFreeA((RPC_CSTR*)&str2);
61 }