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C++-入门语法(五)
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内容图文
仿函数（函数对象）
- 仿函数：将一个对象当作一个函数一样来使用
- 对比普通函数，它作为对象可以保存状态
#include <iostream>
using namespace std;
//int sum(int a, int b) {
// return a + b;
//}
class Sum {
int m_age;
public:
Sum(int age) :m_age(age) { }
int operator()(int a, int b) {
if (this->m_age > 10) {
}
else {
}
return a + b;
}
};
class Point {
friend ostream &operator<<(ostream &, const Point &);
public:
int m_x;
int m_y;
Point(int x, int y) :m_x(x), m_y(y) { }
};
// output stream
ostream &operator<<(ostream &cout, const Point &point) {
return cout << "(" << point.m_x << ", " << point.m_y << ")";
}
// input stream
istream &operator>>(istream &cin, Point &point) {
return cin >> point.m_x >> point.m_y;
}
int main() {
Point p1(10, 20);
cin >> p1;
cout << p1 << endl;
// Sum sum(20);
// cout << sum(10, 20) << endl;
// cout << sum.operator()(10, 20) << endl;
getchar();
getchar();
return 0;
}
运算符重载注意点
- 有些运算符不可以被重载，比如
- 对象成员访问运算符：
- 域运算符：::
- 三目运算符：?:
- sizeof
- 有些运算符只能重载为成员函数，比如
- 赋值运算符：=
- 下标运算符：[ ]
- 函数运算符：( )
- 指针访问成员：->
模板（template）
- 泛型，是一种将类型参数化以达到代码复用的技术，C++中使用模板来实现泛型
- 模板的使用格式如下
- template <typename\class T>
- typename和class是等价的
- 模板没有被使用时，是不会被实例化出来的
- 模板的声明和实现如果分离到.h和.cpp中，会导致链接错误
- 一般将模板的声明和实现统一放到一个.hpp文件中
模板-Array
#include <iostream>
using namespace std;
template <class Item>
class Array {
friend ostream &operator<<<>(ostream &, const Array<Item> &);
int m_size = 0;
int m_capacity = 0;
Item *m_data = NULL;
public:
Array(int capacity);
~Array();
void add(Item value);
Item get(int index);
int size();
Item operator[](int index);
void display();
};
template <class Item>
Array<Item>::Array(int capacity) {
if (capacity <= 0) return;
this->m_data = new Item[capacity]{};
this->m_capacity = capacity;
}
template <class Item>
Array<Item>::~Array() {
if (!this->m_data) return;
delete[] this->m_data;
this->m_data = NULL;
}
template <class Item>
void Array<Item>::add(Item value) {
if (this->m_size == this->m_capacity) {
// 扩容
cout << "数组已满" << endl;
return;
}
this->m_data[this->m_size++] = value;
}
template <class Item>
Item Array<Item>::get(int index) {
if (index < 0 || index >= this->m_size) return 0;
return this->m_data[index];
}
template <class Item>
int Array<Item>::size() {
return this->m_size;
}
template <class Item>
Item Array<Item>::operator[](int index) {
return get(index);
}
template <class Item>
void Array<Item>::display() {
cout << "[";
for (int i = 0; i < this->m_size; i++) {
cout << this->m_data[i];
if (i != this->m_size - 1) {
cout << ", ";
}
}
cout << "]" << endl;
}
template <class Item>
ostream &operator<<<>(ostream &cout, const Array<Item> &array) {
cout << "[";
for (int i = 0; i < array.m_size; i++) {
cout << array.m_data[i];
if (i != array.m_size - 1) {
cout << ", ";
}
}
return cout << "]";
}
#include <iostream>
#include "Array.hpp"
using namespace std;
//template <class Item>
//class Array {
// // friend ostream &operator<<(ostream &, const Array &);
// int m_size = 0;
// int m_capacity = 0;
// Item *m_data = NULL;
//public:
// Array(int capacity) {
// if (capacity <= 0) return;
//
// this->m_data = new Item[capacity] {};
// this->m_capacity = capacity;
// }
//
// ~Array() {
// if (!this->m_data) return;
//
// delete[] this->m_data;
// this->m_data = NULL;
// }
//
// void add(Item value) {
// if (this->m_size == this->m_capacity) {
// // 扩容
// cout << "数组已满" << endl;
// return;
// }
// this->m_data[this->m_size++] = value;
// }
//
// Item get(int index) {
// if (index < 0 || index >= this->m_size) return 0;
// return this->m_data[index];
// }
//
// int size() {
// return this->m_size;
// }
//
// Item operator[](int index) {
// return get(index);
// }
//
// void display() {
// cout << "[";
// for (int i = 0; i < this->m_size; i++) {
// cout << this->m_data[i];
// if (i != this->m_size - 1) {
// cout << ", ";
// }
// }
// cout << "]" << endl;
// }
//};
//ostream &operator<<(ostream &cout, const Array &array) {
// cout << "[";
// for (int i = 0; i < array.m_size; i++) {
// cout << array.m_data[i];
// if (i != array.m_size - 1) {
// cout << ", ";
// }
// }
// return cout << "]";
//}
class Person {
friend ostream &operator<<(ostream &, const Person &);
int m_age;
public:
Person(int age = 0) :m_age(age) { }
};
ostream &operator<<(ostream &cout, const Person &person) {
return cout << "age=" << person.m_age;
}
int main() {
/*Array<Person *> array(3);
array.add(new Person(11));
array.add(new Person(12));
array.add(new Person(13));
array.display();*/
Array<Person> array(3);
array.add(Person(11));
array.add(Person(12));
array.add(Person(13));
// array.display();
cout << array << endl;
/*Array<int> array(5);
array.add(11);
array.add(22);
array.add(33);
array.add(44);
array.add(55);
array.display();
Array<double> array2(3);
array2.add(10.8);
array2.add(10.9);
array2.add(10.4);
array2.display();*/
// cout << array << endl;
/*Array array;
array.add(10);
array.add(20);
array.add(11);
array.add(22);
array.get(2);
array[2];
array.size() == 4;
array.remove(3);
array.insert(1, 30);*/
getchar();
return 0;
}
#include "Swap.h"
//void swapValues(int &v1, int &v2) {
// int tmp = v1;
// v1 = v2;
// v2 = tmp;
//}
//
//void swapValues(double &v1, double &v2) {
// double tmp = v1;
// v1 = v2;
// v2 = tmp;
//}
#pragma once
// template <class T> void swapValues(T &v1, T &v2);
template <class T>
void swapValues(T &v1, T &v2) {
T tmp = v1;
v1 = v2;
v2 = tmp;
}
//void swapValues(int &v1, int &v2);
//void swapValues(double &v1, double &v2);
#pragma once
template <class T> void swapValues(T &v1, T &v2) {
T tmp = v1;
v1 = v2;
v2 = tmp;
}
#include <iostream>
#include "Swap.hpp"
using namespace std;
void test() {
double a = 20.8;
double b = 30.4;
swapValues(a, b);
cout << "test() a = " << a << ", b = " << b << endl;
}
类型转换
- C语言风格的类型转换符
- (type)expression
- type(expression)
- C++中有4个类型转换符
- static_cast
- dynamic_cast
- reinterpret_cast
- const_cast
- 使用格式：xx_cast(expression)
#include <iostream>
using namespace std;
class Person {
public:
int m_age;
virtual void run() { }
};
class Student : public Person {
public:
int m_score;
};
class Car {
};
void test1const_cast() {
const Person *p1 = new Person();
Person *p2 = const_cast<Person *>(p1);
Person *p3 = (Person *)p1;
p2->m_age = 20;
p3->m_age = 30;
cout << p1->m_age << endl;
}
void test2dynamic_cast() {
Person *p1 = new Person();
Person *p2 = new Student();
/*Student *stu1 = (Student *) p1;
Student *stu2 = (Student *) p2;
Car *car = (Car *) p2;*/
Student *stu1 = dynamic_cast<Student *>(p1);
Student *stu2 = dynamic_cast<Student *>(p2);
Car *car = dynamic_cast<Car *>(p2);
cout << stu1 << endl;
cout << stu2 << endl;
cout << car << endl;
}
void test3static_cast() {
Person *p1 = new Person();
Person *p2 = new Student();
Student *stu1 = static_cast<Student *>(p1);
Student *stu2 = static_cast<Student *>(p2);
int i = 10;
double d = i;
cout << stu1 << endl;
cout << stu2 << endl;
}
int main() {
/*int a = 10;
double d1 = (double) a;
double d2 = double(a);
cout << d1 << endl;
cout << d2 << endl;*/
/*Person *p1 = new Person();
Person *p2 = new Student();
Student *stu1 = reinterpret_cast<Student *>(p1);
Student *stu2 = reinterpret_cast<Student *>(p2);
Car *car = reinterpret_cast<Car *>(p2);
cout << p1 << endl;
cout << p2 << endl;
cout << p2 << endl;
cout << stu1 << endl;
cout << stu2 << endl;
cout << car << endl;*/
//// 0a 00 00 00
//int i = 10;
//// 00 00 00 00 00 00 24 40
//double d = i;
//double d1 = 10.0;
//int i1 = d1;
// 0a 00 00 00
// int i = 10;
// 0a 00 00 00 cc cc cc cc
// double d = reinterpret_cast<double&>(i);
// cout << i << endl;
// cout << d << endl;
/*int *p = reinterpret_cast<int *>(100);
int i = reinterpret_cast<int>(p);*/
//cout << "i = " << i << endl;
//cout << "d = " << d << endl;
//cout << sizeof(i) << endl;
//cout << sizeof(d) << endl;
getchar();
return 0;
}
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