Dynamic memory allocation in Fortran90.
! This is a simple example of dynamic memory allocation
! in Fortran90,
! J.D. Wright 1998
real, pointer, dimension (:) :: w1, w2
integer :: i, sizemem
write (unit=*, fmt="(a)") "How big?"
read (unit=*, fmt="(i10)") sizemem
allocate (w1(sizemem), w2(sizemem))
do i = 1, (sizemem)
w1 (i) = i
w2 (i) = i
print *, w1 (sizemem), w2 (sizemem)
end program mem
Dynamic memory allocation in Fortran 77.
This is for comparison with Fortran90, this code is non standard but
works on many systems eg SGI, IBM, Cray, however it does not work (yet!!)
pointer (p1, fred)
pointer (p2, jack)
print *,'How big?'
p1 = malloc(4*size)
p2 = malloc(4*size)
One of the problems with these schemes is you have to still know how much to allocate
before filling the arrays. One of the ways I get around this is to have allocate a block
of 100 fill that, when that is filled I then allocate a second array which is 200, copy
the first 100 to the second array then fill the 2nd half of that array. For 300
do the same. Seems pretty inefficent to me however but there we go. Also a problem in that
at one point I will need (2xrequired) -100 units of memory allocated. Another way is
if I am reading a file that I don't know how long it is I will read it line by line to
the end work out how much I need to allocate, allocate it rewind the file and reread,
nasty but it works.
Last update: Tue Mar 10 17:06:05 CST 1998
Comments to: jon _at_ sinica.edu.tw
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