[英]Can't store lua return value in C++
I have this C++ code that needs to call a Lua function. When I get the function return values, all is well and good ("Even printing the result") but when it comes to storing the variable, the value will disappear.我有这个 C++ 代码需要调用 Lua function。当我得到 function 返回值时,一切都很好(“甚至打印结果”)但是当涉及到存储变量时,该值将消失。
LS = luaL_newstate();
luaL_openlibs(LS);
lua_register(LS, "lua_HostFunction", Link::lua_HostFunction);
if (luaL_dofile(LS, "./src/solutions/16t20.lua") != LUA_OK) {
cout << "Error: File not found or invalid" << endl;
}
string pholder = "prob"+to_string(pi);
lua_getglobal(LS, cv.stringToChar(pholder));
if (!lua_isfunction(LS, -1)) {
cout << pholder << endl;
}
int argNum = 1;
switch(pi) {
case 18: {
char *ptr = strtok(ca, ":");
lua_pushstring(LS, ptr);
ptr = strtok(NULL, ":");
lua_pushstring(LS, ptr);
argNum = 2;
break;
}
default: {
lua_pushstring(LS, ca);
argNum = 1;
break;
}
}
if (lua_pcall(LS, argNum, 1, 0) != LUA_OK) {
cout << "Couldn't call function | " + pholder << endl;
}
if (!lua_isstring(LS, -1)) {
cout << "Not a string";
}
const char* answer = lua_tostring(LS, -1);
// Will print output, but never store
cout << answer << endl;
answers += answer;
lua_pop(LS, 1);
const char* answer = lua_tostring(LS, -1);
lua_tostring returns a pointer to a string in Lua VM. lua_tostring 返回一个指向 Lua VM 中的字符串的指针。
Lua is a language with GC, so this string will disappear after you pop it from Lua API stack: Lua 是一种带有 GC 的语言,所以这个字符串在你从 Lua API 堆栈中弹出后就会消失:
lua_pop(LS, 1);
You end up with a dangling pointer.你最终得到了一个悬垂的指针。
How to fix:怎么修:
Copy string's content somewhere before popping Lua string from Lua API stack.在从 Lua API 堆栈弹出 Lua 字符串之前,将字符串的内容复制到某处。
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