1、本文将使用void lua_pushcclosure (lua_State *L, lua_CFunction fn, int n); 来讲解在Lua Code中注册C函数,其他注册方式将在下一篇文章中讲解。
When a C function is created, it is possible to associate some values with it, thus creating a C closure ;these values are then accessible to the function whenever it is called.To associate values with a C function, first these values should be pushed onto the stack (when there are multiple values, the first value is pushed first).Then lua_pushcclosure is called to create and push the C function onto the stack, with the argument n telling how many values should be associated with the function.lua_pushcclosure also pops these values from the stack.The maximum value for n is 255.
void lua_pushcclosure (lua_State *L, lua_CFunction fn, int n);
Pushes a new Cclosure onto the stack.
当C函数创建时,可以通过c closure 关联一些值,这些值被称作upvalues.当C函数在任何时候被调用,都可以在C函数内部获取到这些值。然后参数n指定 c closure的数量。 n最大值为255个为了关联c closure和C函数,首先把要关联的C closure压入到虚拟栈上面。
在Lua 5.1 Reference Manual 3.4 – C Closures 有详细说明。
2、第一个例子为在Lua Code中注册函数到全局变量中。
//在Lua Code中注册的函数int sum(lua_State *L){int top =lua_gettop(L);int sum =0;for(size_t t=top;t>0;t–){int lnum =lua_tonumber(L,t); sum+=lnum;}lua_pushnumber(L,sum);return 1;}//通过lua_pushcclosure()方法来在Lua Code中注册C函数//lua_pushcclosure()函数是Lua C API提供注册C函数最基础的。其他注册方式都是在该函数上面拓展的。//typedef int (*lua_CFunction) (lua_State *L); 为注册C函数的标准形式// lua_pushcclosure() 中参数n为提供闭包upvalues值的数量void register_sum(lua_State *L){ lua_settop(L,0);int n =0;lua_pushcclosure (L, sum, n);lua_setglobal(L,"sum");}在Lua Code中调用C函数,并打印结果值：
print("sample_3.lua")local a=sum(1,2,3,4,5)print("a:"..a)3、下面例子，是在上面例子的基础上,增加了闭包。
//在Lua Code中注册的函数int sum_closure(lua_State *L){ //到该函数被调用时,可以通过lua_upvalueindex()函数获取到该函数的closureint c1 =(int)lua_tonumber(L, lua_upvalueindex(1));int c2 =(int)lua_tonumber(L, lua_upvalueindex(2));int top =lua_gettop(L);int sum =c1+c2;for(size_t t=top;t>0;t–){int lnum =lua_tonumber(L,t); sum+=lnum;}//把结果值压入虚拟栈返回lua_pushnumber(L,sum);return 1;}//提供upvaluesvoid register_sum_closure(lua_State *L){ lua_settop(L,0);//与sum_closure()函数管理的closure管理的值lua_pushnumber(L,100);lua_pushnumber(L,2000);int n =2; //指定与sum_closure()函数管理的upvalue数量lua_pushcclosure (L, sum_closure, n);lua_setglobal(L,"sum_closure");}在Lua Code中调用C函数
local c =sum_closure(1,2,3,4,5)print("c="..c)int main(int argc, char **argv){ //创建lua_Statelua_State *L = lua_open(); /* create state *///注册标准库luaL_openlibs (L);//注册sum 函数到全局变量中 _G["sum"]register_sum(L);//注册sum_closure(),包括2个upvalueregister_sum_closure(L);//执行sample_1.lualuaL_dofile (L, "sample_3.lua");lua_close(L);return 1;}
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