軟件設(shè)計(jì)（II）教學(xué)課件：Chapter13 Exception Handling

1、Chapter 13 Exception Handling (異常處理)13.1 Introduction13.2 Exception Handling Mechanism13.3 Throwing Mechanisms13.4 Catching Mechanisms13.5 Rethrowing an Exception 13.6 Specifying Exception113.1 IntroductionA program to read in two integers and displays their quotient2QuotientRunint main() cout num1

2、num2; cout num1/num2 is (num1 / num2) endl; return 0;If you enter “0” for num2, then?A runtime error!An exception!Whats Exception?Peculiar problems other than logic or syntax errorsRun time anomalies or unusual conditionsUsually cause the program terminate abnormallyIncluding:ldivision by zero,lacce

3、ss to an array outside of its bounds, or lrunning out of memory or disk space,letc.3Naive Exception HandlingExample of Integer DivisionlAdding an if statement to test the second number4 if (num2 != 0) cout num1 / num2 is (num1 / num2) endl; else cout Divisor cannot be zeroendl;QuotientWithIfRun13.2

4、Exception Handling MechanismSpecial Mechanism to detect, report and act against exceptions.Four taskslFind the problem(Hit the exception)lInform that an error has occurred (Throw the exception)lReceive the error information (Catch the exception)lTake corrective actions (Handle the exception)5Try-thr

5、ow-catchThe try block:lTo preface a block of statements which may generate exceptions.The throw statement:lTo report the exception by throwing a object.The catch block:lTo catche the exception thrown and take actions to handle it.6 try blockDetects and throwsan exception catch blockCatches and handl

6、esthe exceptionException objectC+ Exception HandlingUsing try-throw-catch7int main() cout num1 num2; try if (num2 = 0) throw num1; cout num1 / num2 is (num1 / num2) endl; catch (int e) cout Exception: an integer e cannot be divided by zero endl; cout Execution continues . side = side; double getSide

7、() return side; private: double side;Notes for Multiple CatchesIf a catch block catches exception objects of a base class, it can catch all the exception objects of the derived classes of that base class.So, a catch block for a base class type should appear after a catch block for a derived class ty

8、pe. try . catch (logic_error &ex) . catch (TriangleException &ex) . (a) Wrong order try . catch (TriangleException &ex) . catch (logic_error &ex) . (b) Correct order 1914.5 Rethrowing an ExceptionAn exception can be rethrownlBy a handlerlFor two reasonsThe current handler cannot proc

9、ess the exception or The current handler wants to let its caller be notified of the exception. The syntax:20try statements; catch (TheException &ex) perform operations before exits; throw;Program 13.5.cpp.htmlException Propagation int main() . try . invoke function1; statement1; catch (Exception

10、1 &ex1) Process ex1; statement2; function1 . try . invoke function2; statement3; catch (Exception2 &ex2) Process ex2; statement4; function2 . try . invoke function3; statement5; catch (Exception3 &ex3) Process ex3; statement6; Exception thrown in function3 Call Stack main main function1

11、main function1 main function1 function2 function2 function3 Invocation Exception 21Exception PropagationAn exception that cant be handled by any of a functions catch blocks is thrown to the callerThe exception is propagated along the reverse order of the function calling2214.6 Specifying ExceptionWh

12、at try-catch block should be provided in a function?Exceptions thrown by lThe function itselflThe functions calledWhat exceptions may be thrown by a function?23Exception SpecificationAlso known as throw listllists exceptions that a function can throw24returnType functionName(parameterList) throw (ex

13、ceptionList);Program 13.6.cpp.htmlTwo Special ListsNo throw listlMay throw any exception!Empty throw listlCant throw any exception!25returnType functionName(parameterList) throw ();returnType functionName(parameterList);Undeclared ExceptionThrowing an exception not declared in the throw list? The fu

14、nction unexpected will be invoked! lA standard C+ functionlNormally terminates the program26Visual studio doesnt satisfy the throw list specification well.Catch All Types of ExceptionsThe exception type may not be able to anticipateTo force a catch block to catch all exceptions thrown:catch() /Statements for processin