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IBM-MAIN - Problem bei Kommunikation zwischen C und COBOL (PCRE)


Re: A possible bug in the IBM Runtimne C library


Bernd Oppolzer <bernd.oppolzer@T-ONLINE.DE>


IBM Mainframe Discussion List <IBM-MAIN@LISTSERV.UA.EDU>


2015.02.20 09:07:32

While I agree on that on a philosophical point of view, what are the real
technical implication of that C design decision?

Every 20 years, when there is a major architecture extension (for example 32 bit
to 64 bit), some work has to be done, when for example long changes the meaning
from 32-bit to 64-bit to keep the applications running. Nowadays it is an error
to use long, if you want a 32 bit value, because it is different on some
platforms, whereas int is 32 bit on almost every relevant platform.

This was different 20 years ago, when int was 16 bits (like short) on certain
relevant platforms, so you had to use long to get 32 bits on every relevant

You have two choices:

a) use the standard type (like int or long) that matches the size you need at
all the platforms that are relevant to you ... this will work normally for a
long period of time, and after that, you will have some work to do to examine
your sources and to keep your application running (see example below), or

b) use own types via typedef, and define them depending on the platform (macro

Here is what I had to do, when I had to convert a large insurance math package
to make it run on a Linux 64-bit platform:

- change all long declarations to int (I did this using a program that changed
all the sources)

- change all "%ld" tags in printf and sprintf etc to "%d" etc (this was also
done using the same program, in fact the program was built from scratch to do
all that and it was refined during the process)

- because all pointers changed the size from 4 to 8 bytes, there were some
dependencies inside the code, where offsets of fields inside structures where
calculated; these calculations had to be eliminated or corrected

Although the number of source lines was in the 1 million area, I got it done
within 3 weeks. I had several thousand regression testcases and a testdriver
which allowed me to test the outcome of the math package before and after the
change on the different platforms (Win 32, Linux 64). Without that, the whole
conversion would not have been possible.

So my conclusion is:

such a migration is a large effort, anyway. You will get changes from the
architecture change anyway, no matter if your "longs" change size or not. It is
a project. PL/1, for example, doesn't even have a 64-bit variant (for example on
z/OS). While I agree that the C language has its flaws, it allows for many
things that other languages don't.

Kind regards


Am 20.02.2015 um 00:17 schrieb S.M.:
>   at 08:18 AM, Z.A. said:
>> I still think that the decision, many decades ago, to leave the
>> actual definition and implementation of short, int, long, etc. to
>> the implementation rather than enforce rules (16, 32, 64 bits) was
>> wrong and shortsighted.
> It was appalling; a reversion to FORTRAN-speak after PL/I showed how
> it should[1] be done. But C is still the best PDP-7 specific language
> ever designed.
> [1] In general; I won't argue the Ada approach versus the PL/I
>      approach, as both let the compiler figure out what storage unit
>      is needed to hold the declared variable.

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