从Lua调用函数时如何处理C ++异常？ [英] How to handle C++ exceptions when calling functions from Lua?

问题描述

我有一个工作的C ++函数，我可以从Lua调用。在这里演示我的问题是一个例子：

  int PushHello（lua_State * L）{
 string str ）; 
 lua_pushlstring（L，str.data（），str.length（））; 
 return 1; 
} 
  

注意：我知道我不必在那里使用字符串变量，但这是有问题的。

这是我的两个问题：

1. 当我从Lua中调用此函数时，string构造函数可能会抛出异常。那是问题吗？ Lua会妥善处理它，放开Lua堆吗？我不这么认为我该如何解决？我需要在所有这些代码周围添加 try / catch 并将异常转换为lua_error？没有更好的解决方案？




2. 另外一个问题，我可能通过将Lua编译为C ++来解决，当 lua_pushlstring（）调用 lua_error（）如果使用longjmp，则不会调用string析构函数。问题解决是通过编译为C ++并抛出异常而不是使用longjmp？

要澄清，可能的解决方案我可以看到问题1将是这样的：

  int PushHello（lua_State * L）{
 string str; 
 try {
 str.assign（Hello）; 
 catch（exception& e）{
 luaL_error（L，e.what（））; 
} 
 lua_pushlstring（L，str.data（），str.length（））; 
 return 1; 
} 
  

但是，这样非常丑陋，容易出错，因为 try / catch 需要添加到很多地方。它可以做为一个宏，并放在可以抛出的每个命令上，但这不会更好。

解决方案

我找到了合理的解决方案。问题是它是否正确。而不是导出（或通过lua_cpcall调用）原始函数 int PushHello（lua_State * L）一个包装器 int SafeFunction&PushHello>（lua_State * L） 被导出/调用。包装器看起来像：

 模板< lua_CFunction func> 
 int SafeFunction（lua_State * L）{
 int result = 0; 
 try {
 result = func（L）; 
} 
 //将描述转换为lua_error 
 catch（exception& e）{
 luaL_error（L，e.what（））; 
} 
 // rethrow lua错误 -  C ++ Lua throws lua_longjmp * 
 catch（lua_longjmp *）{
 throw; 
} 
 //任何其他异常作为lua_error没有描述
 catch（...）{
 luaL_error（L，未知错误）; 
} 
 
返回结果; 
} 
  

你觉得怎么样？你有什么问题吗？

I have a working C++ function that I am able to call from Lua. To demonstrate my problem here is an example:

int PushHello(lua_State *L){
    string str("Hello");
    lua_pushlstring(L, str.data(), str.length());
    return 1;
}

Note: I know I don't have to use string variable there, but it is there to demonstrate the problem.

Here are my two problems:

1. When I call this function from Lua string constructor may throw an exception. Is that a problem? Will Lua handle it and unwind the Lua stack properly? I don't think so. How can I solve that? Do I need to add try/catch around all such code and convert the exception to lua_error? Is not there a better solution?

2. Another problem that I have probably solved by compiling Lua as C++ is when lua_pushlstring() calls lua_error() string destructor would not be called if longjmp was used. Is the problem solved by compiling as C++ and throwing exceptions instead of using longjmp?

To clarify, possible solution I can see to problem 1 would be this:

int PushHello(lua_State *L){
    string str;
    try{
        str.assign("Hello");
    catch(exception &e){
        luaL_error(L, e.what());
    }
    lua_pushlstring(L, str.data(), str.length());
    return 1;
}

But that is very ugly and error prone as try/catch would need to be added to many places. It could be done as a macro and put around every command that can throw, but that would not be much nicer.

解决方案

I have found a reasonable solution. The question is whether it is correct. Instead of exporting (or calling via lua_cpcall) the original function int PushHello(lua_State *L) a wrapper int SafeFunction<PushHello>(lua_State *L) is exported/called. The wrapper looks like:

template<lua_CFunction func>
int SafeFunction(lua_State *L){
    int result = 0;
    try{
        result = func(L);
    }
    // transform exception with description into lua_error
    catch(exception &e){
        luaL_error(L, e.what());
    }
    // rethrow lua error - C++ Lua throws lua_longjmp*
    catch(lua_longjmp*){
        throw;
    }
    // any other exception as lua_error with no description
    catch(...){
        luaL_error(L, "Unknown error");
    }

    return result;
}

What do you think about it? Do you see any problems?

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