- 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
- qid_t PL_open_query(module_t ctx, int flags, predicate_t p, term_t +t0)
-
Opens a query and returns an identifier for it. ctx is the context module of the goal. When
NULL, the context module of the calling context will be used, oruserif there is no calling context (as may happen in embedded systems). Note that the context module only matters for meta-predicates. See meta_predicate/1, context_module/1 and module_transparent/1. The term reference t0 is the first of a vector of term references as returned by PL_new_term_refs(n). Raise a resource exception and returns(qid_t)0on failure.Every use of PL_open_query() must have a corresponding call to PL_cut_query() or PL_close_query() before the foreign predicate returns either
TRUEorFALSE.The flags arguments provides some additional options concerning debugging and exception handling. It is a bitwise or of the following values below. Note that exception propagation is defined by the flags
PL_Q_NORMAL,PL_Q_CATCH_EXCEPTIONandPL_Q_PASS_EXCEPTION. Exactly one of these flags must be specified (if none of them is specified, the behavior is as ifPL_Q_NODEBUGis specified)..PL_Q_NORMAL- Normal operation. It is named "normal" because it makes a call to Prolog behave as it did before exceptions were implemented, i.e., an error (now uncaught exception) triggers the debugger. See