Passing a subset of an array to a subroutine without creating a temporary array

1

Dear all,

I wonder if there is a way of passing a non-contiguous subset of a multi-dimensional array to a subroutine while avoiding the creation of a temporary copy of the array in runtime, and without changing the subroutine (e.g. for interfacing with an external library).

Thanks!

3

Thanks, @pmk!

then there shouldn’t be a temporary unless the actual argument has a vector valued subscript or is the result of a function.

To be sure I understand, there is no way I can avoid the temporary copy if I pass to a subroutine a subset of an array arr with extents (1:n,1:n) as follows: call foo(arr(2:n-1,2:n-1)), correct?

5

Actually assumed-type alone (like C’s (void *) ) is not sufficient. Assumed-shape, assumed-rank, pointer and allocatable all get passed by descriptor that can describe a non-contiguous array section. Declaring the dummy argument CONTIGUOUS will also trigger a copy if the actual is not contiguous. As noted before, this is for “normal” sections, not vector subscripts. All of assumed-shape, assumed-rank, pointer, allocatable, or contiguous arguments require a visible interface.

It is helpful, if known, to declare the dummy as INTENT(IN) or INTENT(OUT). That can eliminate on of the copies if the interface can be determined by the compiler.

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