CODEWITHSUNDEEP
pointersmemory-managementfortranfortran90
SkypeMeSM
SkypeMeSM

Reputation: 3287

Fortran 90 array pass by reference issue

What happens if I allocate a F90 pointer thus:

real, pointer :: abc(:)

allocate abc (nx*ny*nz)

I pass abc to a subroutine, where i redefine it as 

real arg1(nx,ny,xz)

This seems to work fine.

But if I redefine as 2D array, I get a segfault.

real arg1(nx,ny)

With reordered arrays as above, it should work. Why does it fail? Any help will be appreciated.

Thanks.

Upvotes: 3

Views: 1505

Answers (2)

steabert
steabert

Reputation: 6918

I don't really understand your problem, what you do should work, since in this case only a reference to the array is passed.

program test
    integer :: nx, ny
    real, pointer :: abc(:)
    nx = 2
    ny = 3
    allocate(abc(nx**3))
    call my_sub(abc, nx, ny)
    write(*,*) abc
end program

subroutine my_sub(abc, nx, ny)
    integer :: nx, ny
    real :: abc(nx,ny)
    abc = 1.0
end subroutine

To know how the arrays are passed, you can read this page. At the bottom you can find a table with possible situations. Here the bottom left case applies.

Upvotes: 3

Jonathan Dursi
Jonathan Dursi

Reputation: 50947

It fails because you're lying to the compiler about the size of the array.

In Fortran 77, people used to use the tricks all the time, because there was no option. In our current enlightened age, we should never do these sorts of tricks -- only Fortran77 and C programmers have to resort to such skulduggery.

As per the answers to changing array dimensions in fortran , if you want to resize an array, or just create a reference to it with a different shape, you can use the RESHAPE intrinsic, or use an array pointer.

Upvotes: 5

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