Sahaj Computer Solutions OOPS WITH C++

Transcription

1 Chapter 8 1

2 Contents Introduction Class Template Class Templates with Multiple Paramters Function Templates Function Template with Multiple Parameters Overloading of Template Function Member Function Templates Non-Type Template Arguments 2

3 Introduction A Template can be used to create a family of classes or functions. For examples, a class template for an array class would be enable us to create arrays of various data types such as intarray and float array. Similarly we can define a template for a function say mul(), that would help us to create various versions of mul() for multiplying int, float and double type values. 3

4 Introduction A template can be considered as macro. When an object of a specify type is defined for actual use, the template definition for that class is substituted with the required data type. Since a template is defined with a parameter that would be replaced by a specified data type at the time of actual use of class or function, the templates are sometimes called parameterized classes or functions. 4

5 Function Template A function template defines a general set of operations that will be applied to various types of data. The type of data that the function will operate upon is passed to it as a parameter. Through a function template, a single general procedure can be applied to a wide range of data. A generic function is created using the keyword template. 5

6 Function Template The general form of a template function definition is shown here: template <class Ttype> return-type func-name(parameter list) { // body of function } Here, Ttype is a placeholder name for a data type used by the function. However, it is only a placeholder that the compiler will automatically replace with an actual data type when it creates a specific version of the function. 6

7 Function Template Example: CH7PG01.CPP The following example creates a generic function that swaps the values of the two variables with which it is called. Because the general process of exchanging two values is independent of the type of the variables, it is a good candidate for being made into a function template. 7

8 Function Template with Multiple Parameters The function template can use more than one generic data type in the template statement, using a commaseparated list as shown below. template<class T1, class T2> returntype function-name(argument of type T1, T2, ) { (body of function). } Example: Ch8pg2.cpp 8

9 Overloading of Template Function A template function may be overloaded either by template function or ordinary functions of its name. This is formally called explicit specialization. In such cases, the overloading resolution is accomplished as follows: Call an ordinary function that has an exact match. Call a template function that could be created with an exact match. Try normal overloading resolution to ordinary functions and call the one that matches. Example: ch8pg3.cpp 9

10 Non Type Template Arguments We have seen that a template can have multiple arguments. It is also possible to use non-member type arguments. That is in addition to the type argument T, we can also use other arguments such as strings, function names, constant expressions and built in types. For Example: template<class T, int size> class array { T a[size]; //automatic array initilization //. }; 10

11 Non Type Template Arguments The arguments that can be passes for the above template are: array<int, 10> a1; // array of 10 integers array<float, 5> a2; //array of 5 floats array<char, 5> a3 ; //String of size 20 Example: Ch8pg4.cpp 11

12 Class Templates A class created from template is called a template class. The class template definition is very similar to an ordinary class definition except the prefix template<class T> and the use of type T. This prefix tells the compiler that we are going to declare a template and use T as a type name in the declaration. 12

13 Class Template Syntax: template <class T> class class-name { //. // class member specification } The syntax for defining an object of template class is: class-name<type> objectname(argslist); Example: CH8PG6.CPP 13

14 Class Template with Multiple Parameters We can use more than one generic type in a class template. They are declared as a comma-separated list within the template specification as shown below template<class T1, class T2> class class-name { //class member specifications } Example: CH8PG7.CPP 14

15 Exception Handling It is very rare that a program is correct at first time. It might have bugs. The two most common types of bugs are logic errors and syntactical errors. The logical errors are due to poor understanding of the problem and solution procedure. The syntactical errors arise due to poor understanding of the language itself. We can detect this bugs by exhaustive debugging and testing procedures. 15

16 Exception Handling The problems which are other than syntactical or logical errors are known as exceptions. Exceptions are runtime anomalies or unusual conditions that a program may encounter while executing. Anomalies might include conditions such as division by zero, access to an array outside of its bounds, or running out of the memory disk space. When such exception occurs it must be necessary to handle it effectively. 16

17 Exception Handling The mechanism suggests a separate error handling code that performs the following tasks: Find the problem ( Hit the program) Inform that an error has occurred( Throw the exception) Receive the error information (catch the exception) Take corrective actions (Handle the exception). 17

18 Basics of Exception Handling Exceptions are of two kinds, namely, synchronous and asynchronous exceptions. Errors such as out of range and over flow belong to the synchronous exceptions. Errors that are caused by evens beyond the control of the program(such as keyboard interrupts) are called asynchronous exceptions. The purpose of exception handling is to handle only synchronous exceptions. 18

19 Exception Handling Mechanism C++ exception handling is built upon three keywords: try, catch, and throw. In the most general terms, program statements that you want to monitor for exceptions are contained in a try block. If an exception (i.e., an error) occurs within the try block, it is thrown (using throw). The exception is caught, using catch, and processed. 19

20 Exception Handling Mechanism Throw point Function that causes exception Throw Exception object Try block Detects and throw an exception Invoke Function Catch block Catches and handles the exception 20

21 General form of exception handling :::::::::::::::::::::::: try {. Throw exception... } catch (type arg) { } //Block of statements which // detects and throws an exception // Catches exception //Block of statements that //handles the exception Example: Ch8PG9.cpp 21

22 Multiple Catch Statements Example: Ch8PG10.cpp It is possible that a program segment has more than one condition to throw an exception. In such cases we can associate more than one catch statement with try block as shown below try { //try block } catch(type1 args) { //catch block1 } catch(type2 args) { //catch block2 } :::::::::::::::::::::::::::::::: catch(typen args) { //catch blockn } 22

23 Throwing Mechanism When an exception that is desired to be handled is detected, it is thrown using the throw statement in one of the following forms: throw(exception ); throw exception; throw; //used for throwing any exception The operand with exception may be of any type, including constants. When a exception is thrown it is caught by the catch statement associated with the try block. That is the control exits the try block, and is transferred to the catch block after that try block. 23

24 Catching all Exceptions In some situations, we may or may not be able to anticipate all possible types of exceptions and therefore may not be able to design independent catch handlers to catch them. In such situation we can force a catch statement to catch all exceptions instead certain type alone. This could be done by using ellipse in the catch block catch( ) { } //statements for processing all exceptions Example: Ch8PG11.cpp 24

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