From: Markus Schöpflin (markus.schoepflin_at_[hidden])
Date: 2002-03-19 10:06:49
> From: "Vesa Karvonen" <vesa_karvonen_at_[hidden]>
> >I'm trying to use the BPL for the following and I'm kind of stuck.
> I have trouble understanding the intention. If you just want a new syntax
> for specifying function types, then I would recommend to not do it. If you
> want a macro for specifying functions types that take N arguments of a
> single type, then there might be some sense. What is it that you are trying
> to macroize?
Ok, I'll explain a little more. I have written a utility header which allows to load DLLs dynamically without much typing for the user. It basically looks like this (of the top of my head...):
class my_dll : public dynamic_dll_loader
DECLARE_FUNCTION_2(__stdcall, int, foo, int, float);
DECLARE_FUNCTION_1(__cdecl, int, bar, double);
my_dll() : dynamic_dll_loader("path_to_my_dll")
The base class takes care of loading and unloading the DLL. The DECLARE_FUNCTION_N makros insert all the necessary declarations and variables and the LOAD_FUNCTION() makros retrieve the function pointers needed.
Later on, you use it like this:
The ultimate goal is to use the BPL to implement the DECLARE_FUNCTION_N makros.
> Are you positive about the syntax of function typedefs that you seem to be
> trying to achieve? The following is a representative of a function
> declaration (of 1 parameter):
> ret_type fun_name(param);
> To get a typedef from any declaration, you just put `typedef´ in front of
> the declaration:
> typedef ret_type fun_type(param);
The following works for me (it's from the DECLARE_FUNCTION_1 makro):
typedef ret_type (cc function_type)(param1);
This gets expanded to
typedef int (__cdecl function_type)(double);
and my compiler (MSVC6SP5) is happy with it.
> Anyway, you obviously need to pass the param to the macro. Try the
> #include <boost/preprocessor.hpp>
> #define MAKE_FUNCTION_TYPE_NAME(f_name)\
> #define MAKE_TYPEDEF_N(ret_type,f_name,n_params,param)\
> typedef ret_type f_name(MAKE_FUNCTION_TYPE_NAME(f_name))\
> #define TYPEDEF_0(ret_type,f_name)\
> #define TYPEDEF_1(ret_type,f_name,param0)\
> The above (probably) isn't what you were after, however. You probably want
> to be able to pass an arbitrary number of parameters:
> And get:
> typedef void bar(bar_type)(foo_type,int,long)
> The above can be done, but I do not understand the motivation. You might
> want to consider using lists.
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