On 5/08/2016 11:11 PM, Frank Swarbrick wrote:
That's good to know. I searched the internet and found a page about implementing dynamic
arrays in C and he was using "double", but 1.5 also sounds reasonable. I
wonder if perhaps there should be some sort of ratcheting down as the number of rows gets
very large.
The C++ runtime library on z/OS is a commercial offering from
Dinkumware. Interestingly they use phi as the growth factor. A lot of
the choices seem to be based on the
properties of the memory allocator. Modern allocators, including z/OS
LE are configurable, so if you plan to use a growth factor of 2 then you
should look into using heap pools.
I have to admire what you're doing. I used to be application programmer
a long time ago and COBOL seriously lacks collection classes that we
take for granted in modern languages.
It would be trivial to write a thin ILC wrapper around the C++ STL to
enable COBOL to use the C++ container classes like vectors, linked
lists, heaps, stacks, queues, maps and hash maps. I'm not sure how much
demand there seems to be for that on the mainframe though.
________________________________
From: IBM Mainframe Discussion List <[email protected]> on behalf of David
Crayford <[email protected]>
Sent: Thursday, August 4, 2016 8:41 PM
To: [email protected]
Subject: Re: COBOL 2014 dynamic capacity tables
On 4/08/2016 2:52 AM, Frank Swarbrick wrote:
Even in the case where it does increase the actual allocated capacity, it does not do it "one
row at a time". Rather, it doubles the current physical capacity and "reallocates"
(using CEECZST) the storage to the new value. This may or may not actually cause LE storage
control to reallocate out of a different area (copying the existing data from the old allocated
area). If there is enough room already it does nothing except increase the amount reserved for
your allocation. And even then, LE has already allocated a probably larger area prior to this from
actual OS storage, depending on the values in the HEAP runtime option.
Almost all the dynamic array implementations that I'm aware of, C++
std::vector, Java ArrayList, Python lists, Lua tables, use a growth
factor of 1.5. Apparently it's a golden ratio.
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