Fortran I/O Read with some error checking

Example

A modern Fortran example which includes error checking and a function to get a new unit number for the file.

module functions

contains

    function get_new_fileunit() result (f)
        implicit none

        logical    :: op
        integer    :: f

        f = 1
        do 
            inquire(f,opened=op)
            if (op .eqv. .false.) exit
            f = f + 1
        enddo

    end function

end module

program file_read
    use functions, only : get_new_fileunit
    implicit none

    integer            :: unitno, ierr, readerr
    logical            :: exists
    real(kind(0.d0))   :: somevalue
    character(len=128) :: filename

    filename = "somefile.txt"

    inquire(file=trim(filename), exist=exists)
    if (exists) then
        unitno = get_new_fileunit()
        open(unitno, file=trim(filename), action="read", iostat=ierr)
        if (ierr .eq. 0) then
            read(unitno, *, iostat=readerr) somevalue
            if (readerr .eq. 0) then
                print*, "Value in file ", trim(filename), " is ", somevalue
            else
                print*, "Error ", readerr, & 
                        " attempting to read file ", & 
                        trim(filename)
            endif
        else
            print*, "Error ", ierr ," attempting to open file ", trim(filename)
            stop
        endif
    else
        print*, "Error -- cannot find file: ", trim(filename)
        stop
    endif

end program file_read