C/C++ Guide

C and C++ bindings ship in the workspace crate ontologos-c (libontologos_c). The stable C ABI is implemented in ontologos-ffi and shared with the .NET bindings.

Install and build

Build from a clone:

# Native library (from repository root)
cargo build -p ontologos-c --release

# C + C++ smoke tests (CMake)
bash crates/ontologos-c/scripts/smoke.sh

Requires a C11 / C++17 toolchain, CMake 3.16+, and Rust.

Headers: crates/ontologos-c/include/ontologos.h (C) and ontologos.hpp (optional C++).

Quick start (C)

#include "ontologos.h"
#include <stdio.h>

ontologos_handle_t reasoner =
    ontologos_reasoner_from_path("family.owl", "rl", 0, -1, 0);
char *report = ontologos_reasoner_classify(reasoner);
if (report) {
    puts(report);
    ontologos_string_free(report);
}
ontologos_reasoner_close(reasoner);

Build in memory:

ontologos_handle_t builder = ontologos_builder_new();
builder = ontologos_builder_add_class(builder, "http://example.org/Pizza");
builder = ontologos_builder_add_class(builder, "http://example.org/Food");
builder = ontologos_builder_subclass_of(
    builder, "http://example.org/Pizza", "http://example.org/Food");
ontologos_handle_t ontology = ontologos_builder_build(builder);
ontologos_handle_t reasoner = ontologos_reasoner_new(ontology, "el", 0, -1);
char *report = ontologos_reasoner_classify(reasoner);
ontologos_string_free(report);
ontologos_reasoner_close(reasoner);
ontologos_ontology_close(ontology);

Quick start (C++)

#include "ontologos.hpp"
#include <iostream>

ontologos::OntologyBuilder builder;
builder.add_class("http://example.org/Pizza")
    .subclass_of("http://example.org/Pizza", "http://example.org/Food");
ontologos::Ontology ontology = builder.build();
ontologos::Reasoner reasoner(ontology, "el");
std::cout << reasoner.classify() << '\n';

The C++ header provides RAII wrappers for common flows; the full API remains in ontologos.h.

File loading

Function	Parse mode	Sandbox	Use when
ontologos_ontology_load	Lenient	No	Trusted local corpora only
ontologos_ontology_load_in	Strict	Yes	User uploads
ontologos_reasoner_from_path	Lenient	No	Trusted paths
ontologos_reasoner_load_in	Strict	Yes	Sandboxed server uploads

For untrusted in-memory input use ontologos_ontology_from_bytes / from_text (strict). Use lenient variants only for trusted corpora.

Resource limits

For JSON snapshots from users:

ontologos_handle_t ontology = ontologos_ontology_from_json_with_limits(
    json, 1048576, -1, -1, -1); /* 1 MiB JSON cap; -1 = default */

Defaults match Limits in ontologos-core.

Errors and memory

• Failures set thread-local errors — read with ontologos_last_error_code() and ontologos_last_error_message(), then ontologos_clear_last_error().
• Strings returned by the library must be freed with ontologos_string_free.
• Handles must be closed with the matching *_close function (or C++ destructors).

API surface

The C API mirrors Python/Node/Java/.NET: classify, check_consistency, is_entailed, query, explain, and incremental axiom helpers. Complex results are JSON strings.

Linking

Platform	Library
macOS	libontologos_c.dylib
Linux	libontologos_c.so
Windows	ontologos_c.dll

Example (Unix):

cc -Icrates/ontologos-c/include app.c -Ltarget/release -lontologos_c -Wl,-rpath,target/release

See Security and Production integration.