C++ Mingw: Two objects of the same class are changing the data across eachother.

Question

I am a newbie. Using class clsMRDateTime and am creating 2 instances of objects in the main code. When I activate the line:

   clsMRDateTime objMRDateTimeURL("10_05_2011");//THIS CAUSES THE PROBLEM!!!!!

It causes the date in the first instance of the class to match the second instance of the class. I checked for static class variables, and cannot figure this out.

I removed all of the inactive methods.

Thank you for any help you can provide. Michael

Sample Test Main():

~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
#include <stdio.h>
#include <string.h>
#include <stdlib.h>
#include <iostream>
#include <fstream>
#include <string>
#include <sstream>
#include "clsMRConvert.h"
#include "clsMRDebug.h"
#include "clsMRDateTime.h"



int main(int argc, char *argv[]) 
{
printf("Content-type: text/html\n\n"); 

cout << "";
cout << "Hello Test";


clsMRDateTime objMRDateTimeToday("08_25_2010");
cout << "<BR>";
string strTodayDate = objMRDateTimeToday.strGetFormatedTime("%m/%d/%Y");
cout << "objMRDateTimeToday: " << strTodayDate;
cout << "<BR>";
cout << "<BR>";

clsMRDateTime objMRDateTimeURL("10_05_2011");//THIS CAUSES THE PROBLEM!!!!!
cout << "<BR>";
//string strURLDate = objMRDateTimeURL.strGetFormatedTime("%m/%d/%Y");
//cout << "objMRDateTimeURL: " << strURLDate;
cout << "<BR>";
cout << "<BR>";


strTodayDate = objMRDateTimeToday.strGetFormatedTime("%m/%d/%Y");
cout << "objMRDateTimeToday: " << strTodayDate << "   [SHOULD BE SAME AS ABOVE!!!]";

}

Class clsMRDateTime:

~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

#include "clsMRDateTime.h"


using namespace std;


clsMRDateTime::clsMRDateTime(string strDateAsString)
 {

 size_t found = strDateAsString.find('_');

 if (found!=string::npos) 
    {
    this->intSetDateTimeURL(strDateAsString);
    }
 else
    {
    }
 }

clsMRDateTime::clsMRDateTime( time_t  timetDateAsTimeT)
    {
this->intSetDateTime(timetDateAsTimeT);
    }




int clsMRDateTime::intSetDateTime(string strDateAsString)
 {

  int intDay, intMonth, intYear;
  sscanf((char *)(strDateAsString.c_str()), "%d/%d/%d", &intMonth, &intDay, &intYear);

    this->timetClassMainTime = this->timetMakeTime(12, 0, 0, 
        intMonth, intDay, intYear);  

    this->tmClassMainTimeTM = this->tmGetTimeInTMFormat();
 }


int clsMRDateTime::intSetDateTimeURL(string strDateAsString)
 {
  int intDay, intMonth, intYear;
  sscanf((char *)(strDateAsString.c_str()), "%d_%d_%d", &intMonth, &intDay, &intYear);

    this->timetClassMainTime = this->timetMakeTime(12, 0, 0, 
        intMonth, intDay, intYear);  

    this->tmClassMainTimeTM = this->tmGetTimeInTMFormat();
 }







int clsMRDateTime::intSetDateTime(time_t  timetDateAsTimeT)
    {
    this->timetClassMainTime = timetDateAsTimeT;
    this->tmClassMainTimeTM = this->tmGetTimeInTMFormat();
    }


int clsMRDateTime::intSetDateTime(struct tm * tmDateAsStructTM)
    {
    this->timetClassMainTime = mktime(tmDateAsStructTM);
    this->tmClassMainTimeTM = this->tmGetTimeInTMFormat();
    }


time_t clsMRDateTime::timetMakeTime(int intHour, int intMin, int intSec, 
                                int intMonth, int intDay, int intYear)
    {

    struct tm * timeinfo;
    time_t time_tSeconds;
    time_t rawtime;


    try{

    //time ( &rawtime );
    timeinfo = localtime ( &this->timetClassMainTime );

    timeinfo->tm_year = intYear-1900;
    timeinfo->tm_mon = intMonth -1;
    timeinfo->tm_mday = intDay;
    timeinfo->tm_hour = intHour; 
    timeinfo->tm_min = intMin;   
    timeinfo->tm_sec = intSec;   
    timeinfo->tm_isdst = 0;

    time_tSeconds = mktime(timeinfo);




        }
    catch (char * str )
    {
         cout << "Exception raised: " << str << '\n';

        return(1);
    }


    return(time_tSeconds);
    }



string clsMRDateTime::strGetFormatedTime(string strFormat)
    {
    string strFormattedTime = "";

    strFormattedTime = this->strGetFormatedTimeForNewDates(strFormat, this->tmClassMainTimeTM);

    return(strFormattedTime);
    }


string clsMRDateTime::strGetFormatedTimeForNewDates(string strFormat, struct tm *tmNewDate)
    {


        string strFormattedTime;
        char s[80];
        size_t i;
        strftime(s,80,strFormat.c_str(),tmNewDate);
        strFormattedTime = s;



    return(strFormattedTime);
    }






time_t clsMRDateTime::timetGetGregoreanTimeStamp()
    {
    return(this->timetClassMainTime);
    }


struct tm *clsMRDateTime::tmGetTimeInTMFormat()
    {

    this->tmClassMainTimeTM = localtime(&this->timetClassMainTime);

    }

Answer 1

You don't show clsMRDateTime.h, but I'm betting in that file you have your member variables declared as static. They shouldn't be.

Answer 2

I would scrutinize any calls to gmtime() or localtime() since they share and reuse a statically allocated structure.

The only other candidate that sticks out is the empty else statement in the first constructor.

Answer 3

clsMRDateTime::tmClassMainTimeTM is a pointer to a struct tm, so when you do this->tmClassMainTimeTM = localtime(&this->timetClassMainTime); you are in fact saving off a pointer to the return value from localtime.

The localtime function reuses a static tm structure, so the return value is the same every time. What you've done is set it up so each instance of clsMRDateTime winds up storing a pointer to the same struct tm so they all end up representing the most recently set date/time.

What you need to do is make tmClassMainTimeTM NOT a pointer (make it just a struct tm) and then do something like this->tmClassMainTimeTM = *localtime(&this->timetClassMainTime);.

Better is to review the man page for localtime_r which is thread safe and allows you to pass in your own struct and use that instead.