System time is represented with the following structure: Instead, it provided three basic structures, two of which will be talked about here and some 20 basic functions to retrieve various time information and convert between various time formats.Īt the heart of the Win32 date and time functionalities, are the SYSTEMTIME and FILETIME structures which are defined in winbase.h as shown: With the Win32 API, Microsoft did not provide any direct functions to calculate time differences or provide capability to compare time values other than file times. We will begin our journey first with the Win32 API functions and then with the MFC functions available. Over years Microsoft has added its own version of date and time functions which this article will now try to cover. In Microsoft C/C++ version 7.0, time returned the current time as the number of seconds elapsed since midnight on December 31, 1899. Struct tm * localtime( const time_t * timer) Īccording to MSDN, in all versions of Microsoft C/C++ except Microsoft C/C++ version 7.0, and in all versions of Microsoft Visual C++, the time function returns the current time as the number of seconds elapsed since midnight on Janu(i.e., epoch). converts the calendar time to the local time to a UTC time represented by the tm structure. converts the calender time represented by timer Struct tm * gmtime( const time_t *timer) The local time or broken-down time which is represented by the tm structure as follows in the time.h header file: The calendar time information in the Standard Library header file can themselves be broken into at least two groups: This article will only deal with calendar times. the calendar time related functions and types as represented by almost everything else in that header file.the CPU related functions and types as represented by clock_t and clock() functions.I like to think of the contents of this file in two portions: As its names indicates, the roots originate in C, so everything is designed in a very C-ish form (i.e., structures, etc.) Our first stop is the ANSI Standard library and the time.h header file. UTC (Coordinated Universal Time): This is the standard international time or the Greenwich Mean Time.Įpoch: Number of seconds elapsed since 00:00:00 on January 1, 1970, Coordinated Universal Time. Some TerminologyĪs always, there are a few jargons that you may have to know about, before getting into this concept, so I thought I should list them right at the beginning: So in this article, I hope to summarize and somewhat simplify the various date and time functionalities in Windows C++. Starting with C and with every library added, there are so many ways to get the date and time that people can easily get confused. Aside from strings, another area where things are probably a little more messy in the C++ and Windows world than it needed to be, has to be the date and time area.
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