c++ - Incorrect result after serializing and deserializing time_t variable

This small program reproduces the bug in my project.
time_t variable is converted to struct_tm, then to string, and serialized to file.
Later, this string is loaded from the file, and should be converted back to time_t.
Resulting time_t differs from original by one hour (possibly because of daylight saving
time). I can change only deserialization part, because file format should remain
unchanged.

#include
            "stdafx.h"
#include 
#include
            
#include 

using namespace
            std;


string FormatDateTime(struct tm*
            time);
void Test();


int _tmain(int argc,
            _TCHAR* argv[])
{
 Test();
 return
            0;
}



string FormatDateTime(struct
            tm* time)
{
 static const char* months[] =
 {

            "Jan", "Feb", "Mar", "Apr", "May", "Jun", "Jul", "Aug", "Sep", "Oct", "Nov",
            "Dec"
 };

 char s[30];

 const char*
            month;

 if ( time->tm_mon >= 0 && time->tm_mon
            < 12 )
 {
 month = months[time->tm_mon];

            }
 else
 {
 month = "??";

            }


 sprintf(s, "%d-%s-%02d %02d:%02d:%02d",

            time->tm_year + 1900,
 month,
 time->tm_mday,

            time->tm_hour,
 time->tm_min,

            time->tm_sec);

 return
            s;

}

void Test()
{
 //
            time_t variable is initialized with current time
 time_t t =
            time(NULL);

 // time_t variable is converted to struct tm and then
            to string
 struct tm* ptm =
            localtime(&t);


 char
            buffer[100];

 sprintf(buffer, "%d %d %d %d %d %d",

            ptm->tm_mday, ptm->tm_mon + 1, ptm->tm_year + 1900, ptm->tm_hour,
            ptm->tm_min, ptm->tm_sec);

 cout << buffer <<
            endl; // string is OK


 // string is saved to the
            file


 //
            *********************************************************************************************


            // later this string is restored from the file

 // **** I can
            change something only after this line **** //

 struct tm
            stm;
 memset(&stm, 0, sizeof(stm));

 sscanf(buffer,
            "%d %d %d %d %d %d",

 &stm.tm_mday, &stm.tm_mon,
            &stm.tm_year, &stm.tm_hour, &stm.tm_min,
            &stm.tm_sec);

 stm.tm_mon -= 1;
 stm.tm_year -=
            1900;

 string s = FormatDateTime(ptm);

 cout
            << s << endl; // OK

 //
            *********************************************************************************************


            // Now I need to convert struct tm to time_t and keep it in the
            variable

 time_t t1 = mktime(&stm); // not the same time - 1
            hour difference

 if ( t1 == t )
 {
 cout
            << "t1 == t" << endl;
 }
 else

            {

 cout << "t1 != t !!!!!" << endl;

            }

 // time_t is printed - result is incorrect


            // Utilities::FormatDateTime
 struct tm* ptm1 =
            localtime(&t1);

 s =
            FormatDateTime(ptm1);


 cout << s <<
            endl;
}

Local time is
11.33. Result:

19 7 2012 11 33
            17
2012-Jul-19 11:33:17
t1 != t
            !!!!!

2012-Jul-19
            12:33:17

How can I change the last
part of this program to get correct result?