C + + uses macros to calculate the number of variable parameters at compile time

Reference https://groups.google.com/forum/#!forum/comp.std.c/d-6Mj5Lko_s

Cppformat source code is also referenced.

C + + is not advocating variable parameters, the reason is not said. But the function families like printf are really handy to use, and I was inadvertently looking at the alternatives to printf. Under the emotion, Microsoft's Cstring::format really is very useful

Cppformat provides printf-like functionality, but is type-safe, with the core of using C + + 's powerful template capabilities. In the implementation, Cppformat implements the calculation of the number of variable parameters at compile time, the principle is https://groups.google.com/forum/#!forum/comp.std.c/d-6Mj5Lko_s inside the discussion

For the sake of brevity, only a maximum of three variable parameters are discussed here.

#define   arg_n (a1,a2,a3,n,...)  N

The function of this macro is to intercept and return the fourth parameter of the argument list

#define  arg_n_helper (...)  Arg_n (__va_args__)

Auxiliary macros, to make the results calculated correctly

#define  count_arg (...)  Arg_n_helper (__va_args__,3,2,1,0)

Calculate the number of variable parameters of the macro, the number of variable parameters is greater than 0, less than or equal to 3 within the range calculated correctly

For example:

1count_arg (x,     y), 2count_arg (count_arg)  , 3 with Count_arg Schematic calculation process Count_arg (x, y), Arg_n_helper (x,y,3,2,1,0), Arg_n (x,y,3,2,1,0)  intercept fourth parameter  2

Also, on the VC compiler, compilation may fail to define the following macro

#define  arg_t (T)  t#define  arg_n_helper (...) arg_t (Arg_n (__va_args__))

The complete macro is as follows

#define ARG_T (t)  t  //Resolve VC Compilation error # define ARG_N (A1,a2,a3,n,...)  N  //Intercept and return a fourth parameter, which limits the range of variable parameter calculations [1,3] #define ARG_N_HELPER (...)  arg_t (Arg_n (__va_args__))   //Auxiliary macro # define COUNT_ARG (...)  Arg_n_helper (__va_args__,3,2,1,0)  //return variable number of parameters

Schematic code

int main () {    int  argn = Count_arg (n/a);//argn value is 3    return 0;}

C + + uses macros to calculate the number of variable parameters at compile time