Learn how to format a returned value such as 1,329,293,701 to a fixed definition of days, months, years, etc.
Earlier this month, over on the RPG Programming section of the IBM i mailing list
First a little background on the stat() API. The stat() IFS API, also known as Get File Information and documented here, returns status information on a given IFS file to an application program. The information returned includes things like type of file (directory, file, symbolic link, etc.), the allocated size of the file, and—of interest today—time values for when the file was last accessed, when the file contents were last changed, and when the status of the file was last changed. The stat() API, along with many of the UNIX-type APIs, returns time information as 4-byte integer values representing the number of seconds since a fixed point in time known as the Epoch. This fixed point in time is defined by the industry as being January 1, 1970 at time 00:00:00 UTC.
Let's say that the stat() API has been called and has returned a value of 1,329,293,701 for the time of last access for a given file. If all we want to do is convert this value to a human-readable format, we can use the Convert Time to a Character String (ctime) API as shown below (where the variable Seconds is initialized to the value returned by the stat() API).
h dftactgrp(*NO) bnddir('QC2LE')
dCTime pr * extproc('ctime')
d SecsAftEpoch 10i 0 const
dSeconds s 10i 0 inz(1329293701)
dTZPtr s *
dTZChar s 26a based(TZPtr)
/free
TZPtr = ctime(Seconds);
dsply TZChar;
*inlr = *on;
return;
/end-free
The preceding program, when compiled and run, will display a message similar to this:
Wed Feb 15 02:15:01 2012
I say "similar to" because the text you actually see can vary due to the time zone your system is running in (my system, being in Rochester, Minnesota, is using United States Central Time), the national language environment your job is running in, and other factors. It's these "factors" influencing the actual text returned by the ctime() API that can make using the API a bit awkward for application programmers. This text approach is fine for display purposes, but trying to make application decisions based on the message text can lead to some rather convoluted programming. Much better, from an application point of view, would be to understand how to format the returned value of 1,329,293,701 to a fixed definition of days, months, years, etc., which is the focus of the remainder of this article.
The ctime() API, by the way, is documented in the ILE C/C++ Run-Time Library Functions manual found here and available on all current systems regardless of whether or not you have the C language compiler installed. And, if your system is at 6.1 or later, you do not need to specify the bnddir('QC2LE') H-spec control keyword that is used in the sample program. The QC2LE binding directory, which is associated with C run-time library functions, is implicitly used by the system when creating programs at 6.1 and later. Also note that you may see a "blob" following the year in the previous message display. This is due to the ctime() API returning a null byte (x'00') at the end of the text string—and the sample program doesn't bother removing this null byte.
One approach to formatting the time value returned by the stat() API is to convert the number of seconds returned by the API to an RPG Timestamp variable as shown in the following program.
h dftactgrp(*NO) bnddir('QC2LE')
dSeconds s 10i 0 inz(1329293701)
dAccessDate s z
dEpoch s z inz(z'1970-01-01-00.00.00')
/free
AccessDate = Epoch + %seconds(Seconds);
dsply %char(AccessDate);
*inlr = *on;
return;
/end-free
This program displays a timestamp value of 2012-02-15-08.15.01.000000 and, from an application program usage point of view, enables you to then use the wealth of date, time, and timestamp operators of RPG to analyze and manipulate the date and time of last access to the IFS file. You might notice, though, that the ctime() API returned a time of 2:15:01 while the RPG Access Date variable shows a time of 8:15:01. The reason for this six-hour difference is that the stat() API is returning a UTC time value, and while the ctime() API automatically adjusts the UTC time to your local time zone, the RPG timestamp operation does not. Assuming that you would prefer to work in local time, there is an API, Get Offset from Universal Time Coordinated to Local Time (CEEUTCO) documented here, that can be used as shown below to retrieve the offset of our local time zone from UTC.
h dftactgrp(*NO) bnddir('QC2LE')
dGetUTCOffset pr extproc('CEEUTCO')
d Hours 10i 0
d Minutes 10i 0
d Seconds 8f
d FC 12a options(*omit)
dSeconds s 10i 0 inz(1329293701)
dAccessDate s z
dUTCOfsHrs s 10i 0
dUTCOfsMins s 10i 0
dUTCOfsSecs s 8f
dEpoch s z inz(z'1970-01-01-00.00.00')
/free
GetUTCOffset(UTCOfsHrs :UTCOfsMins :UTCOfsSecs :*omit);
AccessDate = Epoch + %seconds(Seconds) + %seconds(%int(UTCOfsSecs));
dsply %char(AccessDate);
*inlr = *on;
return;
/end-free
By adding in the local time zones offset from UTC, in seconds, to AccessDate, the sample program now displays a time zone value of 2012-02-15-02.15.01.000000—the local time of last access to the IFS file. In case you're wondering why I used the UTC offset in seconds, as opposed to hours, there are a few time zones in the world where the offset is not an integer number of hours. Using seconds when making local time zone adjustments allows the program to function correctly in many geographical locations without requiring local customizations.
A second approach to formatting the returned value of 1,329,293,701 is using the Convert Time (localtime) API. This API, documented in the ILE C/C++ Run-Time Library Functions manual found here, converts a UTC time value to a data structure comprised of integer subfields defining the date and time in terms of seconds, minutes, hours, days, years, etc. as shown by the data structure TM in the following program.
h dftactgrp(*NO) bnddir('QC2LE')
dLocalTime pr * extproc('localtime')
d SecsAftEpoch 10i 0 const
dSeconds s 10i 0 inz(1329293701)
dTMPtr s *
dTM ds based(TMPtr)
d SecsOfMinute 10i 0
d MinutesOfHour 10i 0
d HourOfDay 10i 0
d DayOfMonth 10i 0
d MthsAftJan 10i 0
d YrsAft1900 10i 0
d DaysAftSun 10i 0
d DaysAftJan1 10i 0
d DSTFlag 10i 0
/free
TMPtr = localtime(Seconds);
dsply %char(SecsOfMinute);
dsply %char(MinutesOfHour);
dsply %char(HourOfDay);
dsply %char(DayOfMonth);
dsply %char(MthsAftJan);
dsply %char(YrsAft1900);
dsply %char(DaysAftSun);
dsply %char(DaysAftJan1);
dsply %char(DSTFlag);
*inlr = *on;
return;
/end-free
The previous program, when run, will display the following information.
DSPLY 1
DSPLY 15
DSPLY 2
DSPLY 15
DSPLY 1
DSPLY 112
DSPLY 3
DSPLY 45
DSPLY -1
The previous displays are showing that the TM data structure subfields of SecsOfMinute (second), MinutesOfHour (minute), HourOfDay (hour), DayOfMonth (day), MthsAftJan (month), YrsAft1900 (year), DaysAftSun (day of week), DaysAftJan1 (day of year), and DSTFlag (Daylight Saving Time) are set to 1, 5, 2, 15, 1, 112, 3, 45, and -1, respectively. In other words, the time is 2:15:01 on Wednesday Feb 15 2012, which happens to be the 46th day of the year. There are a few items I would like to point out about these fields. First, several of the subfields are defined as being base 0. For instance, the MthsAftJan will be set to the value of 0 for January rather than the 1 you might expect (meaning a value of 1 indicates the month of February, one month after January); Sunday is represented by the DaysAftSun value of 0, and January 1 is considered day 0 of the returned year. Second, you may (or may not) be surprised by seeing (infrequently) some minutes having 60 or 61 seconds rather than the expected 0 – 59 seconds after the minute. These additional seconds are to accommodate leap seconds, which the i does support right along with leap days (that we're all familiar with).
Returning to the first program of this article, where the ctime() API created a textual representation of a time value, while automatically adjusting the input UTC time value to local time, there is also the Convert Time to Character String (asctime) API, which will take as input a structure such as our TM data structure and then return a character string representation of the time without making any time zone adjustments. Using this API as shown below will also result in the character string Wed Feb 15 02:15:01 2012 being displayed.
h dftactgrp(*NO) bnddir('QC2LE')
dLocalTime pr * extproc('localtime')
d SecsAftEpoch 10i 0 const
dASCTime pr * extproc('asctime')
d TMStruct like(TM)
dSeconds s 10i 0 inz(1329293701)
dTZPtr s *
dTZChar s 26a based(TZPtr)
dTMPtr s *
dTM ds based(TMPtr)
d SecsOfMinute 10i 0
d MinutesOfHour 10i 0
d HourOfDay 10i 0
d DayOfMonth 10i 0
d MthsAftJan 10i 0
d YrsAft1900 10i 0
d DaysAftSun 10i 0
d DaysAftJan1 10i 0
d DSTFlag 10i 0
/free
TMPtr = localtime(Seconds);
TZPtr = asctime(TM);
dsply TZChar;
*inlr = *on;
return;
/end-free
If you work very often with the UNIX-type APIs, where the IFS APIs are simply one member of the UNIX-type family of APIs, you will find that Epoch-based time values can show up most anyplace. This article hopefully provides you with a few approaches as to how you can work with these Epoch time values in an easy, familiar, and productive manner.
As usual, if you have any API questions, send them to me at
Bruce Vining is president and co-founder of Bruce Vining Services, LLC, a firm providing contract programming and consulting services to the System i community. He began his career in 1979 as an IBM Systems Engineer in St. Louis, Missouri, and then transferred to Rochester, Minnesota, in 1985, where he continues to reside. From 1992 until leaving IBM in 2007, Bruce was a member of the System Design Control Group responsible for OS/400 and i5/OS areas such as System APIs, Globalization, and Software Serviceability. He is also the designer of Control Language for Files (CLF).A frequent speaker and writer, Bruce can be reached at
MC Press books written by Bruce Vining available now on the MC Press Bookstore.
 |
||
 |
|
IBM System i APIs at Work Leverage the power of APIs with this definitive resource. List Price $89.95 Now On Sale
|
More than ever, there is a demand for IT to deliver innovation. Your IBM i has been an essential part of your business operations for years. However, your organization may struggle to maintain the current system and implement new projects. The thousands of customers we've worked with and surveyed state that expectations regarding the digital footprint and vision of the company are not aligned with the current IT environment.
TRY the one package that solves all your document design and printing challenges on all your platforms. Produce bar code labels, electronic forms, ad hoc reports, and RFID tags – without programming! MarkMagic is the only document design and print solution that combines report writing, WYSIWYG label and forms design, and conditional printing in one integrated product. Make sure your data survives when catastrophe hits. Request your trial now! Request Now.
Forms of ransomware has been around for over 30 years, and with more and more organizations suffering attacks each year, it continues to endure. What has made ransomware such a durable threat and what is the best way to combat it? In order to prevent ransomware, organizations must first understand how it works.
Disaster protection is vital to every business. Yet, it often consists of patched together procedures that are prone to error. From automatic backups to data encryption to media management, Robot automates the routine (yet often complex) tasks of iSeries backup and recovery, saving you time and money and making the process safer and more reliable. Automate your backups with the Robot Backup and Recovery Solution. Key features include:
Business users want new applications now. Market and regulatory pressures require faster application updates and delivery into production. Your IBM i developers may be approaching retirement, and you see no sure way to fill their positions with experienced developers. In addition, you may be caught between maintaining your existing applications and the uncertainty of moving to something new.
IT managers hoping to find new IBM i talent are discovering that the pool of experienced RPG programmers and operators or administrators with intimate knowledge of the operating system and the applications that run on it is small. This begs the question: How will you manage the platform that supports such a big part of your business? This guide offers strategies and software suggestions to help you plan IT staffing and resources and smooth the transition after your AS/400 talent retires. Read on to learn:
LATEST COMMENTS
MC Press Online