lua-cpp绑定

sol2
这个目前看比较适合

lua 直接包含源码进来就可以了，不用编译成库。
下面是一个小例子

function sum(x, y)
    return x + y
end

#include <lua/lua.hpp>

int LuaHelper::test(int x, int y)
{
	string strErr;
	lua_State* L = luaL_newstate();
	if (luaL_loadfile(L, "sum.lua") || lua_pcall(L, 0, 0, 0)) {
		strErr = "Error: failed to load sum.lua";
		return 0;
	}

	lua_getglobal(L, "sum");
	lua_pushnumber(L, x);
	lua_pushnumber(L, y);

	lua_pcall(L, 2, 1, 0);

	int result = (int)lua_tonumber(L, -1);
	lua_pop(L, 1);
	return result;
}

读取 lua 数据

void lua_pushnil      (lua_State *L);
void lua_pushboolean  (lua_State *L, int bool);
void lua_pushnumber   (lua_State *L, lua_Number n);
void lua_pushinteger  (lua_State *L, lua_Integer n);
void lua_pushlstring  (lua_State *L, const char *s, size_t len);
void lua_pushstring   (lua_State *L, const char *s);

全局变量

C 接口

int lua_getglobal (lua_State *L, const char *name);
Pushes onto the stack the value of the global name. Returns the type of that value.

void lua_setglobal (lua_State *L, const char *name);
Pops a value from the stack and sets it as the new value of global name.

cpp 读取 lua 表

if (lua_istable(m_luaState,-1))
{
	// Push another reference to the table on top of the stack (so we know
	// where it is, and this function can work for negative, positive and
	// pseudo indices
	lua_pushvalue(m_luaState, -1);
	// stack now contains: -1 => table
	lua_pushnil(m_luaState);
	// stack now contains: -1 => nil; -2 => table
	while (lua_next(m_luaState, -2))
	{
		// stack now contains: -1 => value; -2 => key; -3 => table
		// copy the key so that lua_tostring does not modify the original
		lua_pushvalue(m_luaState, -2);
		// stack now contains: -1 => key; -2 => value; -3 => key; -4 => table
		string strKey = lua_tostring(m_luaState, -1);
		retVar = lua_tonumber(m_luaState, -2);
		// pop value + copy of key, leaving original key
		lua_pop(m_luaState, 2);
		// stack now contains: -1 => key; -2 => table
	}
	
}

栈操作

默认栈空间是 20 个。一般情况下都可以用。

可以使用下面函数检查栈空间是否可用。

-- 返回错误码
int lua_checkstack (lua_State *L, int sz);
-- 返回错误信息
void luaL_checkstack (lua_State *L, int sz, const char *msg);

第一个压栈的元素索引是 1，第二个是 2，以此类推。
引用栈顶元素是 -1，第二个是 -2， 以此类推。

lua_tostring(L, -1) 作为字符串返回栈顶元素

判断栈元素类型，使用一组 lua_is* 函数，* 可以是任何 lua 数据类型。例如：lua_isnil, lua_isnumber, lua_isstring, lua_istable

函数原型如下：
int lua_is* (lua_State *L, int index);

实际上 lua_isnumber 和 lua_isstring 检查的是，能否转换到指定类型。所以 任何数值类型满足字符串类型的判断。

还有个函数 lua_type 可以获取数据类型，每个数据类型都有常量定义：LUA_TNIL, LUA_TBOOLEAN, LUA_TNUMBER, LUA_TSTRING

获取元素个数

获取栈中的元素个数
int lua_gettop (lua_State *L);

放入数据

函数原型：lua_push*
放置 * 元素到栈顶

lua_pushboolean
lua_pushcclosure
lua_pushcfunction
lua_pushfstring
lua_pushinteger
lua_pushlightuserdata
lua_pushliteral
lua_pushlstring （arbitrary strings (char *)）
lua_pushnil
lua_pushnumber （double）
lua_pushstring （zero-terminated strings）
lua_pushthread
lua_pushvalue
lua_pushvfstring

放入数组

// 建一个新表 栈高度+1, 栈顶元素是新table
// 创建一个新的table, 并把它放在栈顶. narr和nrec分别指定该table的array部分和hash部分的预分配元素数量
void lua_createtable (lua_State *L, int narr, int nrec)

// 用于设置table元素的方法
void lua_settable (lua_State *L, int index);
void lua_rawset (lua_State *L, int index);
 
void lua_setfield (lua_State *L, int index, const char *k);
void lua_rawseti (lua_State *L, int index, int n);

类型判断

函数原型：lua_is*

int lua_isstring(lua_State L, int index)
判断index指明位置上的元素是为对应的类型，这里是string. 如果是则返回1，否则返回0；不会改变栈的大小，内容

获取数据

使用 lua_to* 函数。

int lua_toboolean (lua_State *L, int index);
const char  *lua_tolstring (lua_State *L, int index, size_t *len);
lua_State   *lua_tothread (lua_State *L, int index);
lua_Number   lua_tonumber  (lua_State *L, int index);
lua_Integer  lua_tointeger (lua_State *L, int index);

lua_tolstring and lua_tothread return NULL for values with incorrect types.
The numeric functions, however, have no way to signal a wrong type, so they simply return zero.

引入的新函数：
lua_Number lua_tonumberx (lua_State *L, int idx, int *isnum);
lua_Integer lua_tointegerx (lua_State *L, int idx, int *isnum);

The out parameter isnum returns a Boolean that indicates whether the Lua value was successfully coerced to the desired type.

int  lua_gettop    (lua_State *L);
void lua_settop    (lua_State *L, int index);
void lua_pushvalue (lua_State *L, int index);
void lua_rotate    (lua_State *L, int index, int n);
void lua_remove    (lua_State *L, int index);
void lua_insert    (lua_State *L, int index);
void lua_replace   (lua_State *L, int index);
void lua_copy      (lua_State *L, int fromidx, int toidx);

double LuaHelper::test_var()
{
	double result = 0;
	string strErr;

	/* opens Lua */
	lua_State* m_luaState = luaL_newstate();
	/* opens the standard libraries */
	luaL_openlibs(m_luaState);
	if (luaL_loadfile(m_luaState, "sum.lua") || lua_pcall(m_luaState, 0, 0, 0)) {
		strErr = lua_tostring(m_luaState, -1);
		lua_pop(m_luaState, 1);  /* pop error message from the stack */
	}
	else
	{
		double up_right1_min = 15.3456;
		double up_left1_max = 10.1324;
		double up_left1_mean = 10.12;
		double down_left1_mean = 7.12;

		lua_pushnumber(m_luaState, up_right1_min);
		lua_setglobal(m_luaState, "up_right1_min");
		lua_pushnumber(m_luaState, up_left1_max);
		lua_setglobal(m_luaState, "up_left1_max");


		// 获取函数，压入栈中  
		lua_getglobal(m_luaState, "solve_formula");
		// 调用函数，调用完成以后，会将返回值压入栈中，2表示参数个数，1表示返回结果个数。  
		int iRet = lua_pcall(m_luaState, 0, 1, 0);
		if (iRet)
		{
			// 调用出错 
			const char* pErrorMsg = lua_tostring(m_luaState, -1);

			lua_close(m_luaState);
			return -1;
		}
		if (lua_isnumber(m_luaState, -1))        //取值输出  
		{
			result = lua_tonumber(m_luaState, -1);
			string str = fmt::format("{}", result);
			lua_pop(m_luaState, 1);
		}

	}
	lua_close(m_luaState);
	return result;
}