# Targets & cross-compilation The same C+ source builds for more than the machine you are on. A `--target` flag selects where the code is headed, and the compiler emits that target's ABI and intrinsics, not the host's. ```bash cpc build --target ios-arm64 cpc check --target android-arm64 cpc --emit-asm --target esp32-xtensa src/pid.cplus ``` `--target` works on `build`, `check`, and the `--emit-ll` / `--emit-ll-opt` / `--emit-asm` / `--emit-obj` emitters. Omitting it builds for `host` and reproduces the previous behavior byte for byte. ## The named targets | Target | What it is | |---|---| | `host` | The machine you are building on (the default). | | `ios-arm64` | iOS device (arm64). | | `ios-arm64-simulator` | iOS Simulator (arm64). | | `android-arm64` | Android (`aarch64-linux-android24`), via the NDK. | | `esp32-xtensa` | Espressif ESP32 (32-bit Xtensa). See [Embedded & ESP32](/docs/embedded). | An unknown name fails with the supported list. A `TargetSpec` (triple, pointer width, endianness, object format, ABI and intrinsic selectors) drives codegen's per-target choices, so HFA classification, struct size buckets, register pairs, `byval`, spin-loop hints, and NEON selection all resolve against the *selected* target. Host output is unchanged. ## Who runs the final link C+ emits objects; for the platforms with their own build systems, that build system owns the final link. `cpc build` of a `[lib]` staticlib writes the object, the archive, and a C header into `target///`. - **iOS** stops at object emission — **Xcode owns the link**. clang gets `-target ` and an `-isysroot` from `xcrun` when available. `[[bin]]` binaries, `cdylib`, `cpc test`, and single-file builds are rejected for the iOS targets, with the supported staticlib flow named in the message. - **Android** emits `aarch64-linux-android24` ELF objects and staticlibs through the NDK's clang (resolved from `$CPC_NDK_CLANG`, `$ANDROID_NDK_HOME` and friends, or the SDK's newest `ndk/`), archived with the NDK's `llvm-ar` (the host `ar` cannot index ELF members). The NDK's clang must report LLVM 19+ (NDK r28.2+). A cross build pins `target triple = ""` into the emitted IR, so a handed-off `.ll` carries its target. Bundled vendor artifacts resolve by the target's stable artifact triple (`vendor//src/lib/arm64-apple-ios/...`); only `host` consults `clang -print-target-triple`. A host-vs-target triple mismatch is reported as **E0862**. ## Verified end to end These are not paper targets. A C+ staticlib linked by NDK clang has run on a Pixel 9 Pro XL emulator; a C+-driven [UIKit](/docs/packages/uikit) screen renders on an iPhone 16 Pro simulator; and a `#[realtime]` controller runs closed-loop on a physical ESP32. The platform UI bindings are [uikit](/docs/packages/uikit) for iOS, [appkit](/docs/packages/appkit) for macOS, and [espidf](/docs/packages/espidf) for the ESP32.