FORTRAN implicit cast when argument association happens in procedures

Question

I am using fortran for a while, but I didn't check the implicit cast issue when using subroutines in fortran. For example

    subroutine printa(a)
        double precision :: a
        ...
    endsubroutine printa

When I called the subroutine

    call printa(1)

I saw error #6633: The type of the actual argument differs from the type of the dummy argument. [1] I know it is because I use an integer instead of a double precision as an input parameter. But I just realized that there is no implicit cast when using subroutines.

If I want a subroutine which handles integer and double precision data, it seems I have to define 2 subroutines for doing these things. Is there a way to make the implicit cast happen (just like the function calling in c)? Or there is another way to make it?

Thanks.

Answer 1

It is fundamental in Fortran that reals (including different precisions) and integers are different and that you need different subroutines to handle them. If you want the convenience of having a single call, similar to Fortran intrinsics such as sin which are implicitly several different functions, you can write the several different procedures and then create a generic interface to select between them. Fortran will then select the correct actual procedure based on the actual arguments, to match the dummy arguments. Here is an example that does it by rank of the array argument: how to write wrapper for 'allocate'. It can also be done, as you wish, by type of the argument.