[Info-vax] date comparison format from a program

[gérard Calliet]

Le 21/05/2019 à 00:03, Stephen Hoffman a écrit :
> On 2019-05-20 16:58:58 +0000, gérard Calliet said:
> 
>> How doing something as simple as that in C, and not using the basic C 
>> rtl (atoi,...) ,
> 
> Um, what do you think I've been grumbling about for the better part of a 
> decade?
> 
> VSI is starting to address the down-revision tooling, but you're headed 
> into the distant past.
> 
> The doc is pretty thin in these and other areas, too:
> http://h30266.www3.hpe.com/odl/i64os/opsys/vmsos84/5763/5763profile_019.html#date_time_chap 
> 
> 
>>  because the idea is introducing normal young people (who don't know 
>> anything but C and Java) to the way something can be done with (very 
>> old) VAX C and VMS run-time, and also introducting The difference 
>> between C strings and string descriptors.
> 
> Descriptors?  I wrote a few articles on that topic, too. And I've been 
> grumbling about the lack of integration of C and C++ with OpenVMS, and 
> about the tooling, and about the archaic frameworks, and about the 
> morass that are descriptors and logical names and itemlists and all the 
> glue code.  It's a trip straight back to the 1980s, particularly the 
> system services.  Most anybody that knows OO will probably recognize 
> descriptors.  They won't like them and they'll think they're way too 
> primitive.  But they'll recognize them.
> 
> Anybody that knows recent C will usually become frustrated by VAX C and 
> K&R, too.  Having ported a bunch of code from K&R forward, I'd rather 
> not have to port code in the other direction...
> 
> 
> Here's a long-winded and older version of a date comparison 
> else-platform (and slightly modified to document the return values), 
> using Objective C:
> https://stackoverflow.com/a/34992094
> 
> 
>     NSString *dateString1 = @"Fri, 22 Jan 2016 10:46:50 +0530";
>     NSString *dateString2 = @"Fri, 22 Jan 2016 10:46:50 +0530";
> 
>     NSDateFormatter *inputFormatter = [[NSDateFormatter alloc] init];
> 
>     [inputFormatter setDateFormat:@"EEE, dd MMM yyyy HH:mm:ss Z"];
> 
>     NSDate *newDate = [inputFormatter dateFromString:dateString1];
>     NSDate *currentDate = [inputFormatter dateFromString:dateString2];
> 
>     NSComparisonResult result = [newDate compare:currentDate]; // 
> comparing two dates
> 
> /*
> NSComparisonResult can be either of these values:
> - NSOrderedAscending (-1) //if date1 < date2
> - NSOrderedSame (0)       //if date1 = date2
> - NSOrderedDescending (1) //if date1 > date2
> */
> 
> 
> 
> As for this case and for converting two date string to epoch and then 
> comparing them, hit Stack Overflow and start reading.  For the folks 
> here on macOS, Dash.app is handy as that has a complete download of 
> Stack Overflow as one of its data sources.
> 
> As for C, you'll probably be using strptime here.
> https://www.ibm.com/support/knowledgecenter/ssw_ibm_i_72/rtref/strpti.htm
> 
> The following shows how to get to seconds...
> http://pubs.opengroup.org/onlinepubs/9699919799/functions/strptime.html
> 
> And as for all of the reasons folks get themselves in a twist when 
> trying to run old versions far past what they should, I'm well aware. 
> I've heard most of the discussions before.  And the folks will have 
> problems, as the servers are never as isolated as the folks believe. Nor 
> are the servers as reliably isolated.  And the older the stuff gets and 
> the further behind it gets, the more expensive it gets.
> 
> 
> 
Thanks for all the references. And, no, I'll not redo the old discussion 
about "the quarrel of the old and the modern"