课件：湖南大学软件学院MINI数据库项目.ppt

编程与应用,outlines,Rational Class Case review friend Functions opeator overload Extension,Classes and Objects II,class Rational /数据成员：分子,分母； int fm; int fz; /成员函数：输出信息； void show(); ;,定义一种数据类型：Rational，支持分数形式的有理数的输入输出和四则运算。 如：3/4 + 1/3 = 7/12 3/4 *1/3 = 1/4,private:,public:,int main() /声明一个有理数类型的对象 Rational r; /输出r的值，调用r的成员函数show r.show(); ,void show() coutfz“/“fmendl;,Rational:,class Rational /增加成员函数：初始化数据成员 ;,要对有理数的分子和分母进行初始化 构造函数,public:,int main() /声明对象时自动调用构造函数 Rational r; /r的值等于初始值0/1 r.show(); ,Rational:Rational() fz = 0; fm = 1;,Rational();,支持多种初始化方式，比如Rational b(1,2)? 构造函数重载,class Rational /增加成员函数：相乘 multiply( ); ;,要对有理数进行乘法运算,public:,int main() Rational a(1,4); Rational b(1,3); Rational c; /调用mutilpy() c = a.multiply(b); ,Rational Rational:multiply(Rational y) Rational result; result.fm = (this-fm) * (y.fm); result.fz = (this-fz) * (y.fz); return result;,Rational,增加加法操作？,Rational,/rational.h class Rational /数据成员声明； /成员函数声明; ;,程序太长。,/rational.cpp /成员函数定义 Rational:Rational() . void Rational:show() . .,int main() Rational a; a.show(); /对象声明 /成员函数的调用 ,User-defined (programmer-defined) types: classes Data (data members) Functions (member functions or methods) Class instance: object class TypeName . ; Member access specifiers public: Accessible wherever object of class in scope private:Accessible only to member functions of class protected: Objects of class After class definition,Class name is new type specifier Operators to access class members operator (.) Object or Reference to object operator (-) Pointers,Review,Class scope Data members, member functions Within class scope Immediately accessible by all member functions Referenced by name Outside class scope Referenced through handles Object name, reference to object, pointer to object Member functions defined outside class Binary scope resolution operator (:) Format for defining member functions ReturnType ClassName:MemberFunctionName( ) ,Review,Constructor function Same name as class Initializes data members Called when object instantiated Several constructors Function overloading No return type Destructor function Same name as class，Preceded with tilde () No return type & No arguments Cannot be overloaded Performs “termination housekeeping”,Review,2019/9/1,10,可编辑,friend Functions,friend function Delaration in classs scope Begin with keyword friend Defined outside classs scope Right to access non-public members format: class A friend B(); Properties of friendship Friendship granted, not taken Class A must explicitly declare function B friend Not symmetric Not transitive,class Rational /增加友元函数：相乘 rational multiply( ); ;,修改乘法运算，使它变成rational类的友元函数,int main() Rational a(1,4); Rational b(1,3); Rational c; c = multiply(a,b); ,Rational multiply(Rational x,Rational y) Rational result; result.fm = (x.fm) * (y.fm); result.fz = (x.fz) * (y.fz); return result;,friend,友元函数不属于该类，是个旁观者，所以每个操作数都必须声明,Rational x,Rational y,通过函数调用来实现相乘，仍然不直观,int main() Rational a(1,4); Rational b(1,3); Rational c; /c = multiply(a,b);/调用友元函数 /c = a.multiply(b);/调用成员函数 c = a * b; ,Overloading operators Create a friend function for the class FunctionName operator followed by symbol operator* for the multiply operator * Can use existing operators with user-defined types,class Rational /增加友元函数：重载乘法运算符* /friend Rational multiply(Rational x,Rational y); ;,实现乘法运算符*的重载，使它支持有理数类型的数据,friend Rational opeator*(Rational x,Rational y);,int main() c = a * b; ,Rational opeator* (Rational x,Rational y) Rational result; result.fm = (x.fm) * (y.fm); result.fz = (x.fz) * (y.fz); return result;,Overloaded needs istream ,实现的重载