hi all,

i have a c++ memory issue that i need a little help with. i run a debian linux box (woody) using g++ 2.95.4.

i have created a custom class "myClass" which does something like this in one of it's methods:

SomeType myArray[aSize];

SomeType is also a custom class, but could be any other datatype such as int or double. "aSize" is determined during runtime.

the problem occurs for large values of "aSize", which leads me to believe that i'm reaching the process' memory limits, and that it is then killed by the OS. i have 2 reasons for this guess:

1. GDB points me to the line where i allocate the array, when the program does crash.
2. i have written 2 testprograms, both of which use "myClass", both of which work on the same data - the difference is, that one is a console-only app, the other has visual output (using QT/openGL). the console app is quite happy with values of "aSize" which may already crash the QT app... though it will also die, if "aSize" is sufficiantly large.

the thing is this: my machine has enough RAM to handle this array - swap isn't even touched! ulimit also says that i have no limits in resources:

uliimit -a gives:

core file size (blocks, -c) 0
data seg size (kbytes, -d) unlimited
file size (blocks, -f) unlimited
max locked memory (kbytes, -l) unlimited
max memory size (kbytes, -m) unlimited
open files (-n) 1024
pipe size (512 bytes, -p) 8
stack size (kbytes, -s) 8192
cpu time (seconds, -t) unlimited
max user processes (-u) 256
virtual memory (kbytes, -v) unlimited

any ideas, anyone?

thanks,

matthias

I'm no expert on memory management, but when you allocate an array in that fashion, you are asking for contiguous memory - that is, all of it has to be in one chunk. You may still have tons of RAM free, but the barrier you are hitting is when you don't have that much contiguous memory available.

If you're needing really large amounts of memory, a more dynamic allocation method might be better - a linked list perhaps? That way, the memory doesn't need to be contiguous.

> You may still have tons of RAM free, but the barrier
> you are hitting is when you don't have that much
> contiguous memory available.

hi wapcaplet,

my thoughts the same... i'm not sure if i can change this,
though, because some of the algorithms i use in my
program require that the data be stored in this way... at least
i can't think of doing it differently right now.

thanks for your help!

matthias

Hi,

do they really rely on an array or just on the access via operator[ ]?
If so you might be able to use an STL Vector instead.

so long...
bruce

hi bruce,

that worked, thanks.

matthias