Big arrays in C procedures
There is a not-very-huge number N such that,
if a procedure declares a local integer array larger than N,
you get a segmentation fault when the procedure is called.
The same holds for multiple arrays
whose total space is equivalent.
Apparently whatever C
uses for automatic variables cannot handle this
magnitude of array on the stack of procedure calls.
I would suggest that you use one of the following methods:
- Declare the large arrays as a local variable in one file,
and as a global variable in all procedures.
This works, but I can see no advantage to it relative to
the following two methods.
- Declare the arrays in the procedures as static.
This retains locality of variables, and is quite simple.
However, the (excessive) storage remains in existence even when
the procedures that use it are not executing.
- Only declare (int **) variables,
and use calloc to get the required space when needed,
returning it when done. This retains locality of
variables without wasting a large chunk of space when the
procedures that use the big arrays are not in use.
There is an added bonus in that you can save much space
for each array by building triangular arrays,
which is not much harder than building square ones when using
C's pointer-vector system.
Dan Hirschberg
Computer Science Department
University of California, Irvine, CA 92697-3435
dan (at) ics.uci.edu
Last modified: Mar 22, 1999