| Pointers to a variable... [message #77375] |
Fri, 26 August 2011 06:17 |
H. Evans
Messages: 18
Registered: December 2009
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Junior Member |
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In other less friendly languages, e.g. C, the pointer points to an
area of memory, which can coincide with a variable. This gives two
methods to access the contents of the variable:
#include <stdio.h>
main() {
int a=5;
int *p;
p = &a;
printf("a=%i, *p=%i\n", a, *p);
a= 10;
printf("a=%i, *p=%i\n", a, *p);
}
outputs:
a=5, *p=5
a=10, *p=10
So, now that IDL has pointers...can a pointer be set to point to a
variable in the same way, i.e. to reference exactly the same memory
space as the variable?
From the examples, I am under the impression that these pointers don't
quite work in the same way, i.e. the pointers don't point to the same
memory space as the variables.
The reason I ask is that there are some very large variables that I'd
rather not duplicate (waste of memory), but would like to group
serially via a pointer array.
As a trivial example:
a = FINDGEN(10000000L)
b = DINDGEN(200000L)
c = REPLICATE( !P, 10000L)
p = PTRARR(3, /ALLOC)
*p[0] = a
*p[1] = b
*p[2] = c
for i=0,n_ELEMENTS(p)-1 DO print,N_ELEMENTS(*p[i])
Is the only solution to create a,b, and c as heap variables in the
first instance and then point p[i] to the heap variable?
Ta.
Hugh
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