关于Stack unwinding

「爱情、让人受尽委屈。」 2022-08-25 05:22 12阅读 0赞

转点资料，用于备忘 @\_@

## Stack unwinding (C++ only) ##

When an exception is thrown and control passes from a try block to a handler, the C++ run time calls destructors for all automatic objects constructed since the beginning of the try block. This process is called *stack unwinding*. The automatic objects are destroyed in reverse order of their construction. (Automatic objects are local objects that have been declared auto or register, or not declared static or extern. An automatic object x is deleted whenever the program exits the block in which x is declared.)

If an exception is thrown during construction of an object consisting of subobjects or array elements, destructors are only called for those subobjects or array elements successfully constructed before the exception was thrown. A destructor for a local static object will only be called if the object was successfully constructed.

If during stack unwinding a destructor throws an exception and that exception is not handled, the terminate() function is called. The following example demonstrates this:

#include 
       
        <
       
        iostream
       
        >
       
        
    
       
        using
       
         
       
        namespace
       
         std;
    
    
       
        struct
       
         E 
       
        ...
       
        {
          
      const char* message;
      E(const char* arg) : message(arg) ...{ }
    }
       
        ;
    
    
       
        void
       
         my_terminate() 
       
        ...
       
        {
          
      cout << "Call to my_terminate" << endl;
    }
       
        ;
    
    
       
        struct
       
         A 
       
        ...
       
        {
          
      A() ...{ cout << "In constructor of A" << endl; }
      ~A() ...{
           
        cout << "In destructor of A" << endl;
        throw E("Exception thrown in ~A()");
      }
    }
       
        ;
    
    
       
        struct
       
         B 
       
        ...
       
        {
          
      B() ...{ cout << "In constructor of B" << endl; }
      ~B() ...{ cout << "In destructor of B" << endl; }
    }
       
        ;
    
    
       
        int
       
         main() 
       
        ...
       
        {
          
      set_terminate(my_terminate);
    
      try ...{
           
        cout << "In try block" << endl;
        A a;
        B b;
        throw("Exception thrown in try block of main()");
      }
      catch (const char* e) ...{
           
        cout << "Exception: " << e << endl;
      }
      catch (...) ...{
           
        cout << "Some exception caught in main()" << endl;
      }
    
      cout << "Resume execution of main()" << endl;
    }

The following is the output of the above example:

In 
       
        try
       
         block
    In constructor of A
    In constructor of B
    In destructor of B
    In destructor of A
    Call to my_terminate
    
    
      
       
     
      
    In the try block, two automatic objects are created: a and b. The try block 
    throws an exception of type const char*. The handler catch (const char* e)
    catches this exception. The C++ run time unwinds the stack, calling the 
    destructors for a and b in reverse order of their construction. The 
    destructor for a throws an exception. Since there is no handler in the 
    program that can handle this exception, the C++ run time calls terminate().
    (The function terminate() calls the function specified as the argument
    to set_terminate(). In this example, terminate() has
    been specified to call my_terminate().)