SWI-Stream.his included before
SWI-Prolog.h. This function can retrieve the data of the blob using PL_blob_data().
Most blobs reference some external data identified by a pointer and
the write() function writes
If this function is not provided, write/1
emits the content of the blob for blobs of type
PL_BLOB_TEXT or a string of the format
> for binary blobs.
- int save(atom_t a, IOSTREAM *s)
- Write the blob to stream s, in an opaque form that is known
only to the blob. If a “save'' function is not provided (that is,
the field is
NULL), the default implementation saves and restores the blob as if it is an array of bytes which may contain null (
SWI-Stream.hdefines a number of PL_qlf_put_*() functions that write data in a machine-independent form that can be read by the corresponding PL_qlf_get_*() functions.
If the “save'' function encounters an error, it should call PL_warning(), raise an exception (see PL_raise_exception()), and return
FALSE.223Details are subject to change. Note that failure to save/restore a blob makes it impossible to compile a file that contains such a blob using qcompile/2 as well as creating a saved state from a program that contains such a blob impossible. Here, contains means that the blob appears in a clause or directive.
- atom_t load(IOSTREAM *s)
- Read the blob from its saved form as written by the “save''
function of the same blob type. If this cannot be done (e.g., a stream
read failure or a corrupted external form), the “load'' function
should call PL_warning(),
then PL_fatal_error(), and return constFALSE.224Details
are subject to change; see the “save'' function. If a “load''
function is not provided (that is, the field is
NULL, the default implementation assumes that the blob was written by the default “save'' - that is, as an array of bytes
SWI-Stream.hdefines a number of PL_qlf_get_*() functions that read data in a machine-independent form, as written by the by the corresponding PL_qlf_put_*() functions.
The atom that the “load'' function returns can be created using PL_new_blob().
- int PL_unregister_blob_type(PL_blob_t *type)
- Unlink the blob type from the registered type and transform the type of
possible living blobs to
unregistered, avoiding further reference to the type structure, functions referred by it, as well as the data. This function returns
TRUEif no blobs of this type existed and
FALSEotherwise. PL_unregister_blob_type() is intended for the uninstall() hook of foreign modules, avoiding further references to the module.
- int PL_register_blob_type(PL_blob_t *type)
- This function does not need to be called explicitly. It is called if needed when a blob is created by PL_unify_blob(), PL_put_blob(), or PL_new_blob().
The blob access functions are similar to the atom accessing functions. Blobs being atoms, the atom functions operate on blobs and vice versa. For clarity and possible future compatibility issues, however, it is not advised to rely on this.