Re: allocatable array *not* equivalent to dynamic allocation?


"glen herrmannsfeldt" <gah@xxxxxxxxxxxxxxxx> wrote in message
news:zsqdnf5YN8ah2uDZnZ2dnUVZ_vSdnZ2d@xxxxxxxxxxxxxx
Craig Powers wrote:

(snip regarding reallocation)

As I understand it (not having looked at it lately), even the "normal"
dynamic memory access of the C++ (1998) standard library uses this form
of extending something. It's just that it gets buried under the hood of
the standard templates, something that isn't so easy to do in F95.

With C, and I believe also C++, it can be done with at most one copy.
As I understand it, to do it in standard Fortran 90 or 95 requires two
copies. Copy to a temporary array, deallocate and allocate a larger
version of the original array, copy the data back, deallocate the
temporary array.

-- glen


program one_copy_reallocate_x
real,pointer :: x(:)
real,allocatable,target :: y(:)
real :: z(91:100) = [91:100]

allocate ( x(90) ) ; x = [1:90]
allocate ( y(size(x)+size(z))) ; y = [x,z] ! 1 copy
x => y
write (*,*) size(x), x(89:91) ! 100 89. 90. 91.
end program


.

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