The dlopen function provides an interface to the dynamic library
    loader to allow shareable images to be loaded and called at run
    time.

    This function does not load a shareable image but rather saves
    its pathname argument for subsequent use by the dlsym function.
    dlsym is the function that actually loads the shareable image
    through a call to LIB$FIND_IMAGE_SYMBOL.

    The pathname argument of the dlopen function must be the name
    of the shareable image. This name is passed as-is by the dlsym
    function to the LIB$FIND_IMAGE_SYMBOL routine as the filename
    argument. No image-name argument is specified in the call
    to LIB$FIND_IMAGE_SYMBOL, so default file specification of
    SYS$SHARE:.EXE is applied to the image name.

    The dlopen function returns a handle that is used by a dlsym or
    dlclose call. If an error occurs, a NULL pointer is returned.