Question

If I initialize a variable in a Fortran declaration statement, that variable implicitly receives a SAVE attribute and the initialization expression will only be executed once.

For example, the following program

program test
implicit none

    call foo()
    call foo()

contains

    subroutine foo ()
        integer :: i = 0

        i = i + 1
        write(*,*) i
    end subroutine foo
 end program test

will print

1
2

Since this is different in many other languages I was wondering why the Fortran standard committee chose this behavior?

Thanks a lot!
Mike

Answer 1

This is mainly due to historical reasons. Old compilers (Fortran IV(66) and before) were implemented to produce programs using mainly static memory. Old machines even didn’t have any stack. Therefore the programs behave, as the variables were defined as save.

The predecessor of the variable initialization, the DATA statement, is more like defining an initial content of static memory (similar to the directives for the data segment in assembly), than the on call variable initialization you may know from C. The syntax became similar to the C variant later.