在 2011-7-23 晚上10:45，"Mike Pall" <
mikelu-1107@mike.de>写道：
> Thomas Lauer wrote:
>> The following code, run under Windows, produces an error message for
>> line 4 which IMHO is misleading at best but more probably spurious?
>>
>> ffi=require('ffi')
>> ffi.cdef('void DebugBreak(void);') -- Any function will do
>> if ffi.C.DebugBreak then print(ffi.C.DebugBreak) end -- OK
>> if ffi.C.DebugBreak~=nil then print(ffi.C.DebugBreak) end
>>
>> luajit.exe: f:\testffi.lua:4: attempt to compare 'void ()' with 'void *'
>
> Well, the error message is correct. You're comparing a function
> with nil (which is treated like a pointer to void here).
>
> But it's debatable whether comparing a function with a pointer
> should be disallowed. In C, functions and function pointers are
> almost universally exchangeable, so I guess this should be
> allowed here. I've changed the semantics in git HEAD.
>
> [But note that neither of two conditionals in your code can ever
> be true. Only nil and false are treated as not-true conditions.
> And GetProcAddress() returns NULL on error, so there cannot be a
> dynamically resolved function with a NULL address.]
>
> --Mike
>
