C API Export

C API Export

What you'll learn

This guide explains how lp export generates a C-facing header, how --library extends that flow, which LP functions become part of the exported API, and which limitations still matter today.

Prerequisites

• Read CLI and Tooling first.
• A working host C compiler is required if you use --library.

Concepts

lp export is aimed at interoperability with native C or C-compatible callers.

Current public workflow:

• parse an LP file
• generate a C API header
• optionally compile a shared library artifact

Header-only export

Generate a header:

lp export api.lp -o demo_api

Result:

• demo_api.h

If -o is omitted, LP uses the LP file basename.

Header plus shared library

Generate both:

lp export api.lp --library -o demo_api

Result in the current implementation:

• demo_api.h
• demo_api.dll

What gets exported

The header generator walks top-level LP function definitions.

Current rules:

• top-level public functions are exported
• private top-level functions are skipped
• top-level function names starting with _ are skipped by convention
• classes are not automatically turned into a documented stable C object API here

Naming convention

Exported symbols are prefixed with lp_.

If your LP function is:

def add(a: int, b: int) -> int:
    return a + b

The generated declaration follows this pattern:

LP_EXTERN int64_t lp_add(int64_t lp_a, int64_t lp_b);

Example LP source

def add(a: int, b: int) -> int:
    return a + b

Generate the API:

lp export add.lp -o add_api
lp export add.lp --library -o add_api

Minimal C integration example

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

int main(void) {
    printf("%lld\n", (long long)lp_add(20, 22));
    return 0;
}

Important implementation details

• The generated header uses __declspec(dllexport) on Windows and visibility attributes elsewhere.
• The current library artifact naming is still .dll in the implementation when --library is requested.
• Parameters without explicit LP type annotations may degrade to less helpful C signatures in exported headers. For stable native interop, prefer explicit parameter and return annotations.

Common errors and limitations

• --library requires a working host C compiler and the runtime include path.
• The current implementation is oriented around C-callable top-level functions, not full class or object export.
• Shared-library naming is not yet normalized across Windows, Linux, and macOS.
• Experimental Python-interoperability paths are unrelated to lp export and are not a replacement for this stable header-generation path.

See also

• CLI and Tooling
• Build and Distribution
• Troubleshooting