C程序設(shè)計教學(xué)課件：CHAPTER 13 EXCEPTION HANDLING

1、C+ Programming CHAPTER 13 EXCEPTION HANDLING 113.1 Exception Handling13.2 Exception Matching 13.3 Constructors and Destructors in Exception Handling213.1 Exception HandlingAn exception is a run-time error caused by some abnormal condition.In C+, a function f can recognize conditions that identify ex

2、ceptions and then signal that an exception has occurred. This signaling process is called throwing an exception.313.1 Exception HandlingOnce thrown, an exception can be caught or handled by a function that invokes f by using a catch block. A catch block is an exception handler that occurs after a tr

3、y block, which is used to indicate interest in exceptions. 413.1 Exception Handling f() h()g()error spreadingfunction invokedcatching and handling errorcause and throw an errorWhy h( ) doest rectify the error?int *p=new int1000513.1 Exception HandlingThe perfect objective was to map exceptions to so

4、me other form of error propagation should a designer choose to do so.Not that it was always best to do so, but that it could be done.613.1 Exception Handlingthrowing exception .throw expression;.catching and handling exceptiontry expressioncatch（exception type） expressioncatch（exception type） expres

5、sion .713.1 Exception HandlingThe keyword throw creates an object that isnt there under normal program execution. Then the object is, in effect, “returned” from the function, even though that object type isnt normally what the function is designed to return.Each catch clause (exception handler) is l

6、ike a little function that takes a single argument of one particular type.813.1 Exception HandlingRemarks:A) Exception is made and thrown by throw block. B) The code segment that could cause an exception will be in the try block. C) The catch block will not invoked if there is not any exception in t

7、ry block, and the code next to the last catch block will be invoked.913.1 Exception HandlingD) If an exception is thrown, type-matched catch block will catch and handle it. E) If no catch block is matched, the function terminate will be invoked automatically and the program is aborted.1013.1 Excepti

8、on HandlingExample:#includeint Div(int x,int y);void main() try cout5/2=Div(5,2)endl;cout8/0=Div(8,0)endl;cout7/1=Div(7,1)endl; catch(int) coutexcept of deviding zero.n; coutthat is ok.n;int Div(int x,int y) if(y=0) throw y; return x/y;Output:5/2=2except of deviding zero.that is ok.Only the type of

9、“y” is matter!1113.2 Exception MatchingYou can list all types of exceptions in the definition of function.Example:void fun( ) throw(A，B，C，D);You can also define a function that can throw any type of exceptions.Example:void fun( ) throw( );1213.3 Constructors and Destructors in Exception HandlingThe

10、C+ Spirit:“ Trust the programmer”.An object comes into being only after it as been constructed.1313.3 Constructors and Destructors in Exception HandlingIf an exception is matched by the catch block, some thing will be done to handle it.A) Initializing the arguments. B) All the objects that have been

11、 constructed in the try block will be destructed automatically. C) The code segment next to the last catch block will be invoked.1413.3 Constructors and Destructors in Exception HandlingExample:class X public:Aa;Bb;Cc;void main( )X x;abc1513.3 Constructors and Destructors in Exception HandlingExampl

12、e:#include void MyFunc( void );class Expt public: Expt( ); Expt( ); const char *ShowReason( ) const return Expt; ;1613.3 Constructors and Destructors in Exception Handlingclass Demo public:Demo( );Demo( );Demo:Demo( ) coutConstructing Demo.endl;Demo:Demo( ) coutDestructing Demo.endl;1713.3 Construct

13、ors and Destructors in Exception Handlingvoid MyFunc( ) Demo D; coutThrow Expt in MyFunc() endl; throw Expt();int main( ) coutIn main function endl; try coutIn try block, MyFunc( ) is invoked endl; MyFunc( ); There will be some errors.1813.3 Constructors and Destructors in Exception Handling catch(

14、Expt E ) coutIn catch block endl; coutCatching the Expt ; coutE.ShowReason()endl; catch( char *str ) coutCatching the other exception：strendl; coutBack to main function endl; return 0;1913.3 Constructors and Destructors in Exception HandlingOutput:In main functionIn try block, MyFunc() is invokedCon

15、structing Demo.Throw Expt in MyFunc()Destructing Demo.In catch blockCatching the Expt ExptBack to main function20Exercise#include int main()void f1();tryf1();catch(double)cout“OK0!”endl;cout“end0”endl;lreturn 0;21void f1()void f2();tryf2();catch(char)cout“OK1!”endl;cout“end1”endl;l22void f2()void f3();tryf3();catch(int)cout“OK2!”endl;cout“end2”endl;l23void f3()double d=0;trythrow d;catch(float)cout“OK3!”endl;cout“end3”endl;l24mainf1()f2()f3()throw dcatch(char)not matchcatch(int)not matchca