NULL if the term contains blobs that cannot be
serialized, such as streams.
These functions are used to implement library library(fastrw)
as well as for storing Prolog terms in external databases such as
BerkeleyDB (library library(bdb)) or RocksDB. The
representation is optimized for plain atoms and numbers.
Records that are used only in the same Prolog process should use PL_record() as this can represent any term, is more compact and faster.
The returned string may be copied. Note that the string may contain null bytes and is not null terminated. The length in bytes is returned in len. After copying, the returned string may be discarded using PL_erase_external().
PL_recorded_external() is used to copy the term represented in the data back to the Prolog stack. PL_recorded_external() can be used on the returned string as well as on a copy.