Effective C++ 笔记 —— Item 8: Prevent exceptions from leaving destructors.

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Destructors should never emit exceptions. If functions called in a destructor may throw, the destructor should catch any exceptions, then swallow them or terminate the program.

1. Terminate the program if close throws, typically by calling abort:

DBConn::~DBConn()
{
    try 
    {
        db.close(); 
    }
    catch (...) {
        // make log entry that the call to close failed;
        std::abort();
    }
}

2. Swallow the exception arising from the call to close:

DBConn::~DBConn()
{
    try 
    { 
        db.close(); 
    }
    catch (...) {
        //make log entry that the call to close failed;
    }
}

If class clients need to be able to react to exceptions thrown during an operation, the class should provide a regular (i.e., non-destructor) function that performs the operation.

class DBConn {
public:
    // ...
    void close() // new function for
    { 
        // client use
        db.close();
        closed = true;
    }
    ~DBConn()
    {
        if (!closed) 
        {
            try 
            { 
                // close the connection
                db.close(); // if the client didn’t
            }
            catch (...) { // if closing fails,
                //make log entry that call to close failed; 
                //note that and ... terminate or swallow
            }
        }
    }
private:
    DBConnection db;
    bool closed;
};

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