C variable-length parameters use-----to write generic calling functions for LUA

1.C Variable length parameter

The parameter list for the frequently used C-language function, printf, contains a description string for the const char*, and a variable-length parameter (...), as follows for the function declaration of printf.

int printf (const char * __restrict, ...)

In Stdarg.h This header file contains some macros that operate on variable length parameters (for example, the x86 platform):

#define VA_START (AP,V) (AP = (va_list) &v + _intsizeof (v))

#define VA_ARG (Ap,t) (* (t *) (AP + = _intsizeof (t))-_intsizeof (t)))

#define VA_END (AP) (AP = (va_list) 0)

Where running Va_start (AP, V) can cause the AP to point to the address of the first parameter of a variable-length parameter list. Where V is the last fixed parameter.

Va_arg (AP,T) points the AP to the next parameter of a variable-length parameter list, and uses the input type T for data-strong conversions, returning a user-required parameter value.

Va_end (AP), the set AP is null.

Detailed variable length parameter explanation see this blog: Imjacob's column--c in the language of printf implementation

Universal call function for Lua in 2.C language

1#include <stdarg.h>2 3 voidCall_va (Const Char* Func,Const Char*Sig,...)4 {5Va_list VL;//defines a variable-length parameter pointer with no initial value6     intNarg;//number of variable-length parameters7     intNres;//number of return values for LUA functions8 9Va_start (Vl,sig);//to point the pointer to the first parameter of the variable-length parameter first addressTenLua_getglobal (L,func);//function into the stack One  A     //---parameters into the stack -      for(narg=0; *sig;narg++)//Traversal Parameters -     { the         //check the stack for space -Lual_checkstack (L,1,"Too many arguments"); -  -         Switch(*sig++) +         { -             //according to the constraint character of the parameter, by type into the stack, d-double i-int s-char* +              Case 'D': ALua_pushnumber (L,va_arg (VL,Double)); at              Break; -              Case 'I': -Lua_pushinteger (L,va_arg (VL,int)); -              Break; -              Case 's': -Lua_pushstring (L,va_arg (VL,Char*)); in              Break; -              Case '>': to             //end of input parameter +             GotoEndargs; -             default: theError (L,"Invalid option (%c)", * (sig-1)); *         } $     }Panax Notoginseng     //---parameters into the stack - Endargs: theNres=strlen (SIG);//expected number of LUA function return values +  A     //Calling Lua functions the     if(Lua_pcall (L,narg,nres,0)!=0) +     { -Error (L,"error calling '%s ':%s", Func,lua_tostring (l,-1)); $     } $  -     //The return value retrieved after the call -     //The Stack index is -1,-2,-3 from the top of the stack, so the stack index of the first result is-nres thenres=-nres; -      while(*Sig)Wuyi     { the         //get the type descriptor for the return value in turn *sig -         Switch(*sig++) Wu         { -              Case 'D': About             if(!Lua_isnumber (l,nres)) $Error (L,"wrong result type"); -*va_arg (VL,Double*)=Lua_tonumber (l,nres); -              Break; -  A              Case 'I': +             if(!Lua_isnumber (l,nres)) theError (L,"wrong result type"); -*va_arg (VL,int*)=Lua_tointeger (l,nres); $              Break; the  the              Case 's': the             if(!lua_isstring (l,nres)) theError (L,"wrong result type"); -*va_arg (VL,Const Char**)=lua_tostring (l,nres); in              Break; the  the             default: AboutError (L,"Invalid option (%c)", * (sig-1)); the         } the         //parameter index of the result +1 thenres++; +     } - Va_end (VL); the Bayi}

Thus, if we need to invoke a LUA function, we only need the following invocation form:

Call_va ("func", "Dd>ds", x,y,&z,&s);

The function named Func, which represents this LUA function, accepts two double, returns a double and a string, ' > ' represents the delimiter for the parameter and the result of the return value.

C variable-length parameters use-----to write generic calling functions for LUA