C++ 读书笔记之 重载 Overloading
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C++ allows you to specify more than one definition for a function name or an operator in the same scope, which is called function overloading and operator overloading respectively.
An overloaded declaration is a declaration that had been declared with the same name as a previously declared declaration in the same scope, except that both declarations have different arguments and obviously different definition (implementation).
When you call an overloaded function or operator, the compiler determines the most appropriate definition to use by comparing the argument types you used to call the function or operator with the parameter types specified in the definitions. The process of selecting the most appropriate overloaded function or operator is called overload resolution.
Function overloading in C++:
You can have multiple definitions for the same function name in the same scope. The definition of the function must differ from each other by the types and/or the number of arguments in the argument list. You can not overload function declarations that differ only by return type.
Following is the example where same function print() is being used to print different data types:
#include <iostream>using namespace std;class printData{ public: void print(int i) { cout << "Printing int: " << i << endl; } void print(double f) { cout << "Printing float: " << f << endl; } void print(char* c) { cout << "Printing character: " << c << endl; }};int main(void){ printData pd; // Call print to print integer pd.print(2013); // Call print to print float pd.print(512.420); // Call print to print character pd.print("Hello overloading!"); return 0;}/***************运行结果:Printing int: 2013Printing float: 512.42Printing character: Hello overloading!Process returned 0 (0x0) execution time : 1.062 sPress any key to continue.***************/
Operators overloading in C++:
You can redefine or overload most of the built-in operators available in C++. Thus a programmer can use operators with user-defined types as well.
Overloaded operators are functions with special names the keyword operator followed by the symbol for the operator being defined. Like any other function, an overloaded operator has a return type and a parameter list.
Box operator+(const Box&);
declares the addition operator that can be used to add two Box objects and returns final Box object. Most overloaded operators may be defined as ordinary non-member functions or as class member functions. In case we define above function as non-member function of a class then we would have to pass two arguments for each operand as follows:
Box operator+(const Box&, const Box&);
Overloadable/Non-overloadableOperators:
Following is the list of operators which can be overloaded:
+-*/%^&|~!,=<><=>=++--<<>>==!=&&||+=-=/=%=^=&=|=*=<<=>>=[]()->->*newnew []deletedelete []Following is the list of operators which can not be overloaded:
::.*.?:Following is the example to show the concept of operator over loading using a member function. Here an object is passed as an argument whose properties will be accessed using this object, the object which will call this operator can be accessed using this operator as explained below:
#include <iostream>using namespace std;class Box{ public: double getVolume(void) { return length * breadth * height; } void setLength( double len ) { length = len; }阿 void setBreadth( double bre ) { breadth = bre; } void setHeight( double hei ) { height = hei; } void print() { cout <<"\n lenth is "<<length <<"\n breadth is "<<breadth <<"\n height is "<<height<<endl; } // Overload + operator to add two Box objects. Box operator+(const Box& b) { Box box; box.length = this->length + b.length; box.breadth = this->breadth + b.breadth; box.height = this->height + b.height; return box; } private: double length; // Length of a box double breadth; // Breadth of a box double height; // Height of a box};// Main function for the programint main( ){ Box Box1; // Declare Box1 of type Box Box Box2; // Declare Box2 of type Box Box Box3; // Declare Box3 of type Box double volume = 0.0; // Store the volume of a box here // box 1 specification Box1.setLength(6.0); Box1.setBreadth(7.0); Box1.setHeight(5.0); Box1.print(); // box 2 specification Box2.setLength(12.0); Box2.setBreadth(13.0); Box2.setHeight(10.0); Box2.print(); // volume of box 1 volume = Box1.getVolume(); cout << "Volume of Box1 : " << volume <<endl; // volume of box 2 volume = Box2.getVolume(); cout << "Volume of Box2 : " << volume <<endl; // Add two object as follows: Box3 = Box1 + Box2; Box3.print(); // volume of box 3 volume = Box3.getVolume(); cout << "Volume of Box3 : " << volume <<endl; return 0;}/**********************程序运行结果如下: lenth is 6 breadth is 7 height is 5 lenth is 12 breadth is 13 height is 10Volume of Box1 : 210Volume of Box2 : 1560 lenth is 18 breadth is 20 height is 15Volume of Box3 : 5400Process returned 0 (0x0) execution time : 0.245 sPress any key to continue.*************************/
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