Victor Azizi v1kko

> gfortran -fimplicit-none -Werror=implicit-interface main.f90 hello_world.f90 -o hello_world
 main.f90:2:31:

   2 |   call hello_world("You there")
     |                               1
 Error: Procedure ‘hello_world’ called with an implicit interface at (1) [-Werror=implicit-interface]

# We will come back to the -fimplicit-none later
> gfortran -c -Werror=implicit-interface hello_world.f90
> gfortran -Werror=implicit-interface main.f90 -o hello_world
main.f90:3:31:

  3 |   call hello_world("You there")
    |                               1
Error: Type mismatch in argument ‘name’ at (1); passed CHARACTER(1) to INTEGER(4)

# create hello_world_mod.mod and hello_world.o
> gfortran -c -fimplicit-none -Werror=implicit-interface hello_world.f90
# create main.o
> gfortran -c -fimplicit-none -Werror=implicit-interface main.f90
# link and create hello_world binary
> gfortran main.o hello_world.o -o hello_world
# Execute the program
> ./hello_world

	program main
	implicit none
	call hello_world("You there")
	contains
	include 'hello_world.f90'
	end program

	program main
	interface
	subroutine hello_world(name)
	character(len=*) :: name
	end subroutine
	end interface
	implicit none
	call hello_world("You there")
	end program

	module hello_world_mod
	contains
	subroutine hello_world(name)
	implicit none
	write(,) "Hello World: ", name
	end subroutine
	end module

	module hello_world_mod
	contains
	subroutine hello_world(name)
	implicit none ! This should be present in all procedures
	character(len=*) :: name

	write(,) "Hello World: ", name
	end subroutine
	end module

	> gfortran main.f90 hello_world.f90 -o hello_world
	> ./hello_world
	Hello World 544567129