How to write a macro to concatenate two symbols without spaces between them?

[Andrew Haley]

Pan ruochen wrote:
> Hi All,
> 
> Here is my code
> ---------------------------------------
> #define TYPE  1x1
> void func_1x1() { ... }
> void func_2x2() { ... }
> void func_3x3() { ... }
> ---------------------------------------
> 
> I want to implement such an macro my_func(), which asscociats with the
> corresponding function automatically
> according to the value of another macro TYPE.  For example, if TYPE is 1x1
> my_func() is expanded to func_1x1()
> and if TYPE is 2x2, my_func() is expanded to func_2x2()
> I tried #define my_func func ## TYPE
> and #define my_func func TYPE. They are not appropriate.
> How should I write this macro my_func()?

#define P(P1, P2) P1 ## P2

#define MY_FUNC(__TYPE) void P(func_, __TYPE) { }

#define TYPE  1x1

#define my_func MY_FUNC(TYPE)

my_func