c ++ lua设置全局变量时出错 [英] c++ lua error on setting global variable

问题描述

我有下面的代码：

lua_State *lua;
lua = lua_open();
luaL_openlibs(lua);

std::string code = "print(gvar)\n"
    "function test()\n"
    "print(gvar)\n"
    "end\n";

if(!luaL_loadstring(lua, code.c_str())){
    if (lua_pcall(lua, 0, 0, 0)){
        const char* error = lua_tostring(lua, -1); 
        lua_pop(lua, 1);
    }
}

lua_pushstring(lua, "100");
lua_setglobal(lua, "gvar");
if (lua_pcall(lua, 0, 0, 0)){
    const char* error = lua_tostring(lua, -1); // returns "attempt to call a nil value"
    lua_pop(lua, 1);
}

lua_close(lua);

调用函数并获取全局变量很好，但是当我尝试设置全局变量时，调用nil值。我不明白为什么是这样？

Calling functions and getting global variables works fine, but when i try to set global variable i get "attempt to call a nil value". And i cant understand why is that?

推荐答案

if(!luaL_loadstring(lua, code.c_str())){
    if (lua_pcall(lua, 0, 0, 0)){
        const char* error = lua_tostring(lua, -1); 
        lua_pop(lua, 1);
    }
}

此代码将字符串加载到匿名函数中使用 luaL_loadstring（），将它放在堆栈上，然后使用 lua_pcall（lua，0，0，0）执行函数。

This code loads string into a anonymous function using luaL_loadstring(), puts it on the stack and then executes the function using lua_pcall(lua, 0, 0, 0).

lua_pushstring(lua, "100");
lua_setglobal(lua, "gvar");
if (lua_pcall(lua, 0, 0, 0)){
    const char* error = lua_tostring(lua, -1); // returns "attempt to call a nil value"
    lua_pop(lua, 1);
}

这段代码将字符串推入堆栈，然后设置全局变量 gvar 。在调用 lua_setglobal（）后，堆栈上应该没有任何东西。

This piece of code pushes string onto the stack then sets global variable gvar. There should be nothing on the stack after call to lua_setglobal(). The var is already there.

现在，您尝试使用 lua_pcall 调用位于堆栈顶部的函数$ c>，但是栈是空的 - 这就是为什么你得到尝试调用一个nil值消息。

Now after that you try to call a function which is at the top of the stack with lua_pcall, but the stack is empty - that's why you get attempt to call a nil value message.

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