Access a C library interface from F90 using iso_c_binding

So, I am trying to access a C function from F90, with the following code:

SUBROUTINE sub1()

    USE,INTRINSIC :: iso_c_binding

    ! interface to c library
    INTERFACE
        ! library function prototype
        ! DBfile *DBCreate (char *pathname, int mode, int target, char *fileinfo, int filetype)
        TYPE(C_PTR) FUNCTION DBCreate_f(pathname,mode,fileformat,fileinfo,filetype) BIND(C,NAME="DBCreate")
            IMPORT :: C_PTR,C_CHAR,C_INT
            IMPLICIT NONE
            CHARACTER(KIND=C_CHAR) :: pathname(*)
            INTEGER(KIND=C_INT),VALUE :: mode
            INTEGER(KIND=C_INT),VALUE :: fileformat
            CHARACTER(KIND=C_CHAR) :: fileinfo(*)
            INTEGER(KIND=C_INT),VALUE :: filetype
        END FUNCTION DBCreate_f

        ! library function prototype
        ! int DBClose (DBfile *dbfile)
        INTEGER(KIND=C_INT) FUNCTION DBClose_f(dbfile) BIND(C,NAME="DBClose")
            IMPORT :: C_INT,C_PTR
            IMPLICIT NONE
            TYPE(C_PTR) :: dbfile
        END FUNCTION DBClose_f
    END INTERFACE


    CHARACTER(LEN=...) :: string11
    CHARACTER(LEN=...,KIND=C_CHAR) :: string1
    INTEGER(C_INT) :: val1,val2,val3
    CHARACTER(LEN=...) :: string21
    CHARACTER(LEN=...,KIND=C_CHAR) :: string2

    TYPE(C_PTR) :: retval1_ptr
    INTEGER(C_INT) :: retval2


    retval1_ptr=C_NULL_PTR


    !======================================================================
    ! call to first interface function
    !======================================================================
    WRITE(string11,FMT='(a)') "blahblahblah"
    WRITE(UNIT=string1,FMT='(a,a)') TRIM(string11),C_NULL_CHAR
    val1=1
    val2=2
    WRITE(string21,FMT='(a)') "BLAHBLAHBLAH"
    WRITE(UNIT=string2,FMT='(a,a)') TRIM(string21),C_NULL_CHAR
    val3=3
    retval1_ptr=DBCreate_f(string1,val1,val2,string2,val3)      ! this is line 372 in the original file
    ! DBCreate returns a DBfile pointer on success and NULL on failure.
    IF (.NOT.C_ASSOCIATED(retval1_ptr)) CALL terminate(...)

    !======================================================================
    ! call to second interface function
    !======================================================================
    retval2=DBClose_f(retval1_ptr)
    ! DBClose returns zero on success and -1 on failure.
    IF (retval2==-1) CALL terminate(...)


END SUBROUTINE sub1

However, in the link stage, I get the error:

module1.o: In function `sub1':

module1.f90:372: undefined reference to `DBCreate'

Several notes:

• It is my understanding that C_PTR can be used to return scalar pointers of _any_ type, and since I don't need to access any of the data pointed at by this pointer directly, I thought the above would be ok.
• There are two calls to the library, and only one of them is having a problem.  However, running nm on the .a file verified that the function DBCreate is actually in the file.
• I tried this with various versions of ifort, from early 12.xxx to 14.xxx, and they all exhibit the same problem.
  
   

Any thoughts?  Thanks.