Re: C vs C++

[Jevgeni Astanovski <jevgeniast@xxxxxxxxx>]

No chance, Charles.
All three are compiled in 2 phases and all three use ACTGRP(*CALLER).


On Mon, Feb 16, 2015 at 5:10 PM, Charles Wilt <charles.wilt@xxxxxxxxx> wrote:
> Any chance your C++ programs are using ACTGRP(*NEW) and the C ones are not?
>
> Charles
>
> On Mon, Feb 16, 2015 at 9:56 AM, Jevgeni Astanovski <jevgeniast@xxxxxxxxx>
> wrote:
>
> > Hi all.
> > Does anyone have any idea why C++ program is significantly slower than
> > C program?
> >
> > Explain the situation.
> > I have a number of API-s that are called via RPC, access some tables,
> > make some calculations and return some structures to the caller.
> > They've all been written on ILE/C.
> > Recently I started to experiment with porting them to ILE/C++. There
> > was a number of reasons why it would be nice.
> > After I rewrote the first one, I started to measure performance. This
> > is an issue for me as some of them are called hundreds of thousands
> > times per day.
> > Found out that it is approximately 2 times slower than C version.
> > Shared a code to colleges - no one found anything suspicious. However
> > one guy came out with a "brilliant" idea - he advised me to try to
> > recompile my C program with CPP compiler and see the performance.
> > Guess what? C program compiled with CPP compiler was the same 2 times
> > slower than C program compiled with C compiler....
> >
> > And the only modifications that I did for compiling C with CPP compiler
> > was:
> > 1. Substituted "#pragma mapinc" table structue definitions with those
> > generated by GENCSRC;
> > 2. Changed char and unsigned char in a couple of places as C++ is more
> > strict;
> > 3. Made a substitution for "NNNND" constants (like 100D for example)
> > as C++ does not support that.
> >
> > What I saw is that time increase looks like it has a proportional nature.
> > I tested API in 3 cases (number of tests is over 100): simple request,
> > medium request; complicated request and the timing is:
> > Simple C: 1ms; Simple C++ : 2ms
> > Medium C: 3ms; Simple C++ : 7ms
> > Long C: 25ms; Long C++: 60ms.
> >
> > The difference is in number of records read from table and a number of
> > calculations.
> > That is a simple one retrieves less that 10 records; medium - more
> > than 10 and long - more than 100. Program makes a lot of calculations
> > with packed decimal.
> >
> > Any idea why it is like that and is there anything that can be done about
> > it?
> >
> > Thanks in advance,
> >
> > Jevgeni.
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