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Import stat.h using LuaJIT

I am writing a Lua application, and I am trying to access the values of the S_IWUSR constant inside the stat.h header file using the FFI library of LuaJIT.

How can I include stat.h in my Lua code so I can access the constant?

Thanks

Solution

  • With ffi.cdef you can load most C code in the FFI C namespace, but there's no preprocessor so far, so you should use enums for constant values.

    In my sys/stat.h S_IWUSR is defined as followed:

    #define _S_IWRITE 0x0080
...
#define _S_IWUSR    _S_IWRITE
...
#define S_IWUSR     _S_IWUSR

    Example with LuaJIT:

    local ffi = require("ffi")

ffi.cdef([[
    enum{S_IWUSR = 0x0080};
]])

print(ffi.C.S_IWUSR) -- 128

    There's also the way with static const variables to add a type.

    static const int S_IWUSR = 0x0080;

    BUT you have to care not to redefine! Remember: there's just one FFI instance per Lua state, require("ffi") doesn't make a new one. It's recommend to put C definitions in a module and let the Lua package system manage loading them just once.