Lua table转string

使用C++实现了几个不同版本的table2string
经过测试后发现:

1. 对于数值类型转字符串, sprintf性能好于std::to_string, stringstream表现不堪入目
2. 直接使用char*要好于std::string, 字符串连接, strcat好于sprintf
3. 对于数值类型, 转为16进制性能略优于10进制但相当有限, 同时可读性会差很多

以下是std::to_string版本, 虽然char*版本性能更好, 但实在没必要, 差距并不大的情况下, 还是照顾下程序可读性吧

// 使用std::string
void table2string(lua_State * L, int index, std::string& str, std::set<const void*>& visited) {
	try {
		lua_pushnil(L);
		str.push_back('{');
		bool is_null = true;
		while (lua_next(L, index)) {
			int ktype = lua_type(L, -2);
			str += "[";
			if (ktype == LUA_TNUMBER) {
				if (lua_isinteger(L, -2)) {
					str += std::to_string(lua_tointeger(L, -2));
				} else if (lua_isnumber(L, -2)) {
					str += std::to_string(lua_tonumber(L, -2));
				}
			} else if (ktype == LUA_TSTRING) {
				str += "\"";
				str += lua_tostring(L, -2);
				str += "\"";
			} else if (ktype == LUA_TBOOLEAN) {
				str += lua_toboolean(L, -2) ? "true" : "false";
			} else {
				char buffer[32] = {0};
				sprintf(buffer, "\"%p\"", lua_topointer(L, -2));
				str += buffer;
			}
			str += "]=";

			int vtype = lua_type(L, -1);
			if (vtype == LUA_TTABLE) {
				const void * p = lua_topointer(L, -1);
				if (visited.count(p)) {
					char buffer[32] = {0};
					sprintf(buffer, "\"%p\":", p);
					str += buffer;
				} else {
					visited.insert(lua_topointer(L, -1));
					table2string(L, lua_gettop(L), str, visited);
				}
			} else if (vtype == LUA_TBOOLEAN) {
				bool b = lua_toboolean(L, -1);
				str += b ? "true" : "false";
			} else if (vtype == LUA_TSTRING) {
				str.push_back('"');
				str += lua_tostring(L, -1);
				str.push_back('"');	
			} else if (vtype == LUA_TNUMBER) {
				if (lua_isinteger(L, -1)) {
					str += std::to_string(lua_tointeger(L, -1));
				} else if (lua_isnumber(L, -1))
					str += std::to_string(lua_tonumber(L, -1));
			} else {
				char buffer[32] = {0};
				sprintf(buffer, "\"%p\"", lua_topointer(L, -1));
				str += buffer;
			}
			str.push_back(',');
			is_null = false;
			lua_pop(L, 1);
		}
		if (!is_null)
			str.pop_back();
		str.push_back('}');
	}
	catch(const std::exception& e) {
		luaL_error(L, e.what());
	}
}

static int TableToString(lua_State * L)
{
	int type = lua_type(L, -1);
	switch (type) {
	case LUA_TNIL:
		lua_pushnil(L);
		break;
	case LUA_TBOOLEAN:
		lua_pushstring(L, lua_toboolean(L, -1) ? "true" : "false");
		break;
	case LUA_TSTRING:
		lua_pushstring(L, lua_tostring(L, -1));
		break;
	case LUA_TNUMBER:
		if (lua_isinteger(L, -1)) {
			lua_pushstring(L, std::to_string(lua_tointeger(L, -1)).c_str());
		} else {
			lua_pushstring(L, std::to_string(lua_tonumber(L, -1)).c_str());
		}
		break;
	case LUA_TTABLE: {
		std::set<const void*> visited;
		visited.insert(lua_topointer(L, -1));
		std::string str;
		str.reserve(512);// 提前分配一段空间, 减少自动扩容次数, 如果大概知道字符串的长度, 可以通过lua设置, 更加灵活
		table2string(L, lua_gettop(L), str, visited);
		lua_pushstring(L, str.c_str());
		}
		break;
	default: {
		char buffer[32] = {0};
		sprintf(buffer, "\"%p\"", lua_topointer(L, -1));
		lua_pushstring(L, buffer);
		}
		break;
	}
	return 1;
}


#define ADD_VALUE(L, index, type, buffer, format) {\
char tmp[32] = {0};\
sprintf(tmp, (format), lua_to##type((L), (index)));\
luaL_addstring(&(buffer), tmp);\
}

// 使用luaL_Buffer
void concattable(lua_State * L, int index, luaL_Buffer& b, std::set<const void*>& visited) {
	try {
		lua_pushnil(L);
		luaL_addchar(&b, '{');
		while (lua_next(L, index)) {
			int ktype = lua_type(L, -2);
			luaL_addchar(&b, '[');
			if (ktype == LUA_TNUMBER) {
				if (lua_isinteger(L, -2)) {
					ADD_VALUE(L, -2, integer, b, "%lld");
				} else if (lua_isnumber(L, -2)) {
					ADD_VALUE(L, -2, number, b, "%0.6lf");
				}
			} else if (ktype == LUA_TSTRING) {
				luaL_addchar(&b, '"');
				luaL_addstring(&b, lua_tostring(L, -2));
				luaL_addchar(&b, '"');
			} else if (ktype == LUA_TBOOLEAN) {
				luaL_addstring(&b, lua_toboolean(L, -2) ? "true" : "false");
			} else {
				ADD_VALUE(L, -2, pointer, b, "\"%p\"");
			}
			luaL_addstring(&b, "]=");

			int vtype = lua_type(L, -1);
			if (vtype == LUA_TTABLE) {
				const void * p = lua_topointer(L, -1);
				if (visited.count(p)) {
					ADD_VALUE(L, -1, pointer, b, "\"%p\"");
				} else {
					visited.insert(lua_topointer(L, -1));
					concattable(L, lua_gettop(L), b, visited);
				}
			} else if (vtype == LUA_TBOOLEAN) {
				luaL_addstring(&b, lua_toboolean(L, -1) ? "true" : "false");
			} else if (vtype == LUA_TSTRING) {
				luaL_addchar(&b, '"');
				luaL_addstring(&b, lua_tostring(L, -1));
				luaL_addchar(&b, '"');
			} else if (vtype == LUA_TNUMBER) {
				if (lua_isinteger(L, -1)) {
					ADD_VALUE(L, -1, integer, b, "%lld");
				} else if (lua_isnumber(L, -1)) {
					ADD_VALUE(L, -1, number, b, "%0.6lf");
				}
			} else {
				ADD_VALUE(L, -1, pointer, b, "\"%p\"");
			}
			luaL_addchar(&b, ',');
			lua_pop(L, 1);
		}
		luaL_addchar(&b, '}');
	}
	catch(const std::exception& e) {
		luaL_error(L, e.what());
	}
}

static int joinstring(lua_State * L) {
	int type = lua_type(L, 1);
	switch (type) {
	case LUA_TNIL:
		lua_pushnil(L);
		break;
	case LUA_TBOOLEAN:
		lua_pushstring(L, lua_toboolean(L, 1) ? "true" : "false");
		break;
	case LUA_TSTRING:
		lua_pushstring(L, lua_tostring(L, 1));
		break;
	case LUA_TNUMBER:
		if (lua_isinteger(L, -1)) {
			lua_pushstring(L, std::to_string(lua_tointeger(L, 1)).c_str());
		} else {
			lua_pushstring(L, std::to_string(lua_tonumber(L, 1)).c_str());
		}
		break;
	case LUA_TTABLE: {
		std::set<const void*> visited;
		visited.insert(lua_topointer(L, 1));
		luaL_Buffer b;
		luaL_buffinit(L, &b);
		concattable(L, 1, b, visited);
		luaL_pushresult(&b);
		}
		break;
	default: {
		char buffer[32] = {0};
		sprintf(buffer, "\"%p\"", lua_topointer(L, 1));
		lua_pushstring(L, buffer);
		}
		break;
	}
	return 1;
}

static const struct luaL_Reg methods[] = {
	{ "tostring", TableToString }, 
	{ "join", joinstring }, 
	{ NULL, NULL }, 
};