Calling a function or subroutine

Question

I'm quite new to fortran, i'm trying to execute a function/subroutine but i'm getting an error Explicit interface required

This is my code:

function printmat(m)
    integer, dimension(:,:) :: m
    integer :: row,col
    row = size(m,1)
    col = size(m,2)
       do k=1,row
            print *, m(k,1:col)
       enddo
end function printmat

program test
    integer, dimension(5, 5) :: mat
    integer :: i,j
    do i=1,5
    do j=1,5
           mat(j,i) = real(i)/real(j)
    enddo
    enddo
    call printmat(mat)
end program test

But when i execute it i get:

Error: Explicit interface required for 'printmat' at (1): assumed-shape argument

Any idea of what could it be? I tried wrapping it into a module, but when i use "use modulename" in the program it gives me an error (tries to read it from a file with the same name)

Answer 1

Wrap it into a module and make it a subroutine if you want to use it with CALL.

module printmat_module
contains
  subroutine printmat(m)
    integer, dimension(:,:) :: m
    integer :: row,col
    row = size(m,1)
    col = size(m,2)
    do k=1,row
       print *, m(k,1:col)
    enddo
  end subroutine printmat
end module printmat_module

program test
  use printmat_module
  integer, dimension(5, 5) :: mat
  integer :: i,j
  do i=1,5
     do j=1,5
        mat(j,i) = real(i)/real(j)
     enddo
  enddo
  call printmat(mat)
end program test

Alternatively you can just do what the compiler tells you and add an explicit interface to the program.

subroutine printmat(m)
  integer, dimension(:,:) :: m
  integer :: row,col
  row = size(m,1)
  col = size(m,2)
  do k=1,row
     print *, m(k,1:col)
  enddo
end subroutine printmat

program test
  interface
     subroutine printmat(m)
       integer, dimension(:,:) :: m
     end subroutine printmat
  end interface
  integer, dimension(5, 5) :: mat
  integer :: i,j
  do i=1,5
     do j=1,5
        mat(j,i) = real(i)/real(j)
     enddo
  enddo
  call printmat(mat)
end program test