C++ ofstream write content to file.ifstream read content from file

#include <iostream>
#include <fstream>
#include <uuid/uuid.h>
#include <ctime>
#include <unistd.h>
#include <sstream>

static char *uuidValue = (char *)malloc(40);

char *getTimeNow()
{
time_t rawTime = time(NULL);
struct tm tmInfo = *localtime(&rawTime);
strftime(dtValue, 20, "%Y%m%d%H%M%S", &tmInfo);
return dtValue;
}

void getUuidValue3(char *uuidValue)
{
uuid_t newUUID;
uuid_generate(newUUID);
uuid_unparse(newUUID, uuidValue);
}

void ifstream18()
{
    ifstream rFile;
    rFile.open("log3.txt",ios::in);
    if(!rFile.is_open())
    {
        cout<<"Open log3.txt failed!"<<endl;
    }

    string line;
    while(getline(rFile,line))
    {
        cout<<line<<endl;
    }
    rFile.close();
    cout<<"Finsihed in ifstream18() and now is "<<getTimeNow()<<endl;
}

void ofstream17()
{
    ofstream wFile;
    wFile.open("log3.txt",ios::app);
    if(!wFile.is_open())
    {
        cout<<"Create or open log2.txt failed!"<<endl;
    }

    for(int i=0;i<1000000;i++)
    {
        getUuidValue3(uuidValue);
        wFile<<i<<","<<uuidValue<<endl;
    }

    free(uuidValue);
    wFile.close();
    cout<<"Close in ofstream17() and now is "<<getTimeNow()<<endl;
}