浙江大学《C++程序设计》课件-chapter14 Smart Pointer.pdf

Object Oriented Programming CHAP14 Smart Pointer 浙江大学《C++程序设计》 Exception specifications • Declare which exceptions function might raise • Part of function prototypes void abc (int a) : throw(MathErr) { ... } • Not checked at compile time • At run time, – if an exception not in the list propagates out, the unexpected exception is raised /55 Failure in constructors: • No return value is possible • Use an “uninitialized flag” • Defer work to an Init() function Better: Throw an exception /55 Failure in constructors... If you constructor can’t complete, throw an exception. • Dtors for objects whose ctor didn’t complete won’t be called. • Clean up allocated resources before throwing. /55 Two stages construction • Do normal work in ctor – Initialize all member objects – Initialize all primitive members – Initialize all pointers to 0 – NEVER request any resource • File • Network connection • Memory • Do addition initialization work in Init() /55 Exceptions and destructors Destructors are called when: • Normal call: object exits from scope • During exceptions: stack unwinding invokes dtors on objects as scope is exited. What happens if an exception is thrown in a destructor? /55 Exceptions and destructors... Throwing an exception in a destructor that is itself being called as the result of an exception will invoke std::terminate(). • Allowing exceptions to escape from destructors should be avoided. /55 Programming with exceptions Prefer catching exc