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Mods in C

A mod is a DLL that exports five functions over the C ABI, so any language that can include a C header can write one: C, C++, Zig, Odin. The header is enshwick.h, written from the same Rust types the loader uses and checked against the ABI’s layout on every change. Here you build the example mod hello.c, which writes one line to the log when it starts.

Write the mod

Section titled “Write the mod”
  1. Copy enshwick.h next to your source file.
  2. Fill a static EnshwickManifest: its header is the struct’s size and ENSHWICK_ABI_VERSION; a mod needs at least id, version and side. ENSHWICK_STR_INIT("text") makes a string.
  3. Define enshwick_mod_abi, enshwick_mod_query, enshwick_mod_init and enshwick_mod_ready; enshwick_mod_shutdown is optional. The header declares them with ENSHWICK_EXPORT, so the DLL exports them.
  4. In enshwick_mod_init, call the loader through the EnshwickHostApi table it passes, such as host->log(me, EnshwickLevel_INFO, line).

Names follow one pattern: Rust’s Status::OK is EnshwickStatus_OK, the type HookSpec is EnshwickHookSpec, and a constant such as MAX_ZONES is ENSHWICK_MAX_ZONES. Every comment in the header is the Rust item’s documentation.

Build it

Section titled “Build it”

On Windows with LLVM, or on Linux and macOS with clang and lld:

Terminal window
clang --target=x86_64-pc-windows-msvc -std=c11 -O2 -shared -fuse-ld=lld \
  hello.c -o hello_c.dll

hello.c uses no C runtime, so it also builds with -ffreestanding -nostdlib -Wl,/NOENTRY and needs no Windows SDK. A mod that calls the C runtime links it as usual: with Visual Studio’s cl /LD, clang-cl or cargo-xwin’s SDK off Windows.

Check it

Section titled “Check it”

Run cargo enshwick manifest hello_c.dll on Windows. It loads the DLL, asks it for its manifest and prints the id, version and side. Then copy the DLL into the game’s mods/ folder. The log shows hello from C under you.hello-c when the loader starts it.

Keep it current

Section titled “Keep it current”

A struct that starts with an EnshwickHeader only grows at its end, and the loader reads your struct only as far as your header says, so a mod built against an older enshwick.h keeps loading. Take a newer header for the newer fields and functions. The ABI reference has the rules.