- Documentation
- Reference manual
- Foreign Language Interface
- The Foreign Include File
- Argument Passing and Control
- Atoms and functors
- Analysing Terms via the Foreign Interface
- Constructing Terms
- Unifying data
- Convenient functions to generate Prolog exceptions
- Serializing and deserializing Prolog terms
- BLOBS: Using atoms to store arbitrary binary data
- Exchanging GMP numbers
- Calling Prolog from C
- Discarding Data
- String buffering
- Foreign Code and Modules
- Prolog exceptions in foreign code
- Catching Signals (Software Interrupts)
- Miscellaneous
- Errors and warnings
- Environment Control from Foreign Code
- Querying Prolog
- Registering Foreign Predicates
- Foreign Code Hooks
- Storing foreign data
- Embedding SWI-Prolog in other applications
- The Foreign Include File
- Foreign Language Interface
- Packages
- Reference manual
/1.
It may be used together with
PL_chars_to_term(),
but the typical use case will create a number of clauses for the same
predicate. The fastest way to achieve this is by creating a term that
represents the invariable structure of the desired clauses using
variables for the variable sub terms. Now we can loop over the data,
binding the variables, asserting the term and undoing the bindings.
Below is an example loading words from a file that contains a word per
line.
#include <SWI-Prolog.h> #include <stdio.h> #include <string.h> #define MAXWLEN 256 static foreign_t load_words(term_t name) { char *fn; if ( PL_get_file_name(name, &fn, PL_FILE_READ) ) { FILE *fd = fopen(fn, "r"); char word[MAXWLEN]; module_t m = PL_new_module(PL_new_atom("words")); term_t cl = PL_new_term_ref(); term_t w = PL_new_term_ref(); fid_t fid; if ( !PL_unify_term(cl, PL_FUNCTOR_CHARS, "word", 1, PL_TERM, w) ) return FALSE; if ( (fid = PL_open_foreign_frame()) ) { while(fgets(word, sizeof word, fd)) { size_t len; if ( (len=strlen(word)) ) { word[len-1] = '\0'; if ( !PL_unify_chars(w, PL_ATOM|REP_MB, (size_t)-1, word) || !PL_assert(cl, m, 0) ) return FALSE; PL_rewind_foreign_frame(fid); } } PL_close_foreign_frame(fid); } fclose(fd); return TRUE; } return FALSE; } install_t install(void) { PL_register_foreign("load_words", 1, load_words, 0); }
12.4.17.4 Getting file names
The function PL_get_file_name() provides access to Prolog filenames and its file-search mechanism described with absolute_file_name/3. Its existence is motivated to realise a uniform interface to deal with file properties, sea