C Interop Guide

Zero supports a small, explicit C ABI export surface. Exported C functions use primitive scalar parameters or explicit references accepted by the native checker.

export c fun add(a: i32, b: i32) -> i32 {    return a + b}

Check the ABI surface:

bin/zero check conformance/native/pass/c-abi-export.0
bin/zero abi dump --json conformance/native/pass/c-abi-export.0

The ABI dump reports exported C symbols and a small generated header text block. For conformance/native/pass/c-abi-export.0, generatedHeader.available is true and the header contains the zero_add declaration.

Invalid export surfaces fail before C emission:

bin/zero check --json conformance/native/fail/bad-c-export.0

Header imports are available as typed metadata:

bin/zero graph --json --target wasm32-web conformance/check/pass/c-header-import.0

The graph JSON exposes cImports[].typedModel with imported functions, constants, structs, enums, and typedefs.

It also includes a cache object keyed by:

header hash
target
ABI
flags hash
sysroot fingerprint

External C calls require target library audit facts. zero graph --json reports each cLibraries[].linkPlan with include paths, library paths, sysroot status, target ABI, and host discovery status.

Cross builds must use package-relative vendored headers/libraries or an explicit target sysroot. They cannot silently reuse host include or library paths.

Unsafe foreign-target discovery fails with CIMP003 before code generation:

bin/zero build --json --target linux-musl-x64 conformance/c/host-leak-package --out .zero/out/host-leak-package