C ++ FSM设计和所有权 [英] C++ FSM design and ownership

问题描述

我想为此语法实现FSM/下推式自动机"解析器:有限状态机解析器

I would like to implement a FSM/"pushdown automaton" parser for this syntax: parser with scopes and conditionals which has already been "lexed" into Finite State Machine parser

我有以下内容:

class State
{
public:
    virtual State* event( const string &token );
    State* deleteDaughter();
private:
    A* m_parent;
    A* m_daughter;
}
class SomeState : public State
{
public:
    State* event( const std::string &token );
}

使用B的event()(在许多if-elseif之后)return m_parent->deleteDaughter().我知道这很腥(并且崩溃了)，但是我需要一种方法来从女儿State返回父亲State，并确保女儿State没有泄漏.

With B's event() doing (after many if-elseif's) return m_parent->deleteDaughter(). I know this is fishy (and it crashes), but I need way to return the parent State from the daughter State and make sure the daughter State isn't leaked.

我的事件循环如下:

while( somestringstream >> token )
    state = state->event();

在责骂设计和最后一段代码之前，我尝试从这里，看起来还不错.为了简洁明了，我将决策部分移至各州本身.

Before you scold the design and last piece of code, I tried extending a much too simple example from here, which seems pretty ok. I am moving the decision part to the states themselves, for clarity and brevity.

我了解关于此主题的书籍很多，但我不是计算机科学家/程序员，我想学习自己做到这一点(当然，在SO的所有友好人员的帮助下).如果概念不清楚，请询问.谢谢！

I understand there's loads of books on this subject, but I'm no computer scientist/programmer and I want to learn to do this myself (of course, with the help of all the friendly people at SO). If the concept isn't clear, please ask. Thanks!

推荐答案

仍然可以发表您的看法，但是我想出了如何优雅地处理所有问题的方法:

Feel free to still post your take on this, but I have figured out how to handle everything gracefully:

首先:我的事件循环将保留指向最后创建的State*的指针.

First: my event loop will keep a pointer to the last State* created.

第二个:每个State都有一个指向父级State的指针，该指针在构造函数中初始化，默认为0(如果用于第一个State*以外的任何内容，则发生内存泄漏)；这保证了任何国家都不会超出范围.

Second: Each State has a pointer to the parent State, initialized in the constructor, defaulting to 0 (memory leak if used for anything but the first State*); this guarantees that no State will go out of scope.

第三项:State* endOfState()函数正是这样做的(我为此感到特别自豪.

Third: State* endOfState() function which does exactly this (and I'm particularly proud of this.

State* State::endOfState()
{
    State* parent = m_parent; // keep member pointer after suicide
    delete this;
    return parent;
}

在子类的event()中调用此方法时，它将正确删除自身，并返回父指针(在梯形图中向上移动).

When this is called from within a subclass's event(), it will properly delete itself, and return the parent pointer (going one up in the ladder).

如果仍然包含泄漏，请通知我.如果解决方案不清楚，请询问:)

If this still contains a leak, please inform me. If the solution is not clear, please ask :)

PS:为了公平起见，灵感来自 http://www .codeguru.com/forum/showthread.php?t = 179284

PS: for all fairness, inspiration was stolen from http://www.codeguru.com/forum/showthread.php?t=179284

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