Creating a FORTRAN interface to a C function that returns a char*

Question

I\'ve been held up on this for about a week, now, and have searched forum after forum for a clear explanation of how to send a char* from C to FORTRAN. To make the matter m

Answer 1

I have also struggled with calling a C routine that returns a string and the answers above has been very useful but as I know almost nothing of C and the answers are slightly confusing I just wanted to contribute my solution which uses a C pointer, I did not manage to make use any of the other proposals above. The C program I call opens a separate window to browse for a file name.

program test
  use iso_c_binding
  implicit none
! A C function that returns a string need a pointer to the array of single char 
  type (c_ptr) :: C_String_ptr
! This is the Fortran equivalent to a string of single char
  character (len=1, kind=c_char), dimension(:), pointer :: filchar=>null()
! Interface to a C routine which opens a window to browse for a file to open
  interface
    function tinyopen(typ) bind(c, name="tinyopen")
       use iso_c_binding
       implicit none
       integer(c_int), value :: typ
       type (C_Ptr) :: tinyopen
    end function tinyopen
  end interface
  character (len=256) :: filename
  integer typ,jj
  typ=1
C_String_ptr = tinyopen(typ)
! convert C pointer to Fortran pointer
  call c_f_pointer(C_String_ptr,filchar,[256])
  filename=' '
  if(.not.associated(filchar)) then
! if no characters give error message
    write(*,*)'No file name'
  else
! convert the array of single characters to a Fortran character
    jj=1
    do while(filchar(jj).ne.c_null_char)
      filename(jj:jj)=filchar(jj)
      jj=jj+1
    enddo
  endif
  write(*,*)'Text is: ',trim(filename)
end program test

Hopefully this example will make it easier for the next one with the same problem.