运算符重载
简易cout、cin的实现
类内重载
//自己写一个命名空间
namespace myspace {
class istream {
public:
//返回对象的引用:为了一直使用这个cin对象，避免再拷贝一份
istream &operator>>(int &n) {
//参数传引用，避免再拷贝一份n
std::cin >> n; //可以用scanf来实现
return *this;
}
private:
};
class ostream {
public:
ostream &operator<<(int &n) {
std::cout << n; //可用printf("%g")来实现
return *this;
}
ostream &operator<<(const char *msg) {
std::cout << msg;
return *this;
}
private:
};
istream cin;
ostream cout;
};
int main() {
int n, m;
myspace::cin >> n >> m; //系统默认为执行 cin.operator>>(n)
myspace::cout << n << " " << m << "\n";
return 0;
}
类外重载
//自己写一个命名空间
namespace myspace {
class istream {
public:
//返回对象的引用:为了一直使用这个cin对象，避免再拷贝一份
istream &operator>>(int &n) {
//参数传引用，避免再拷贝一份n
std::cin >> n;
return *this;
}
private:
};
class ostream {
public:
ostream &operator<<(int &n) {
std::cout << n;
return *this;
}
ostream &operator<<(const char *msg) {
std::cout << msg;
return *this;
}
private:
};
istream cin;
ostream cout;
};
//类外重载运算符
myspace::ostream &operator<<(myspace::ostream &out, double &z) {
std::cout << z;
return out;
}
ostream &operator+(ostream &out, const int &a) {
//这时的a不仅可以是传过来的常量(子面量)也可以是变量
cout << a;
return out;
}
int main() {
int n, m;
//cin >> n: 系统会将其转化为 cin.oprator>>(n)
myspace::cin >> n >> m;
myspace::cout << n << " " << m << "\n";
double k = 5.5;
myspace::cout << k << "\n";
(((((cout + 8) << " ") + 9 )<< " ") + 10) << "\n"; //要注意 + 和 << 的优先级
return 0;
}
重载实战
//重载运算符的方法的参数个数一定要和原来运算符的目数相同
//优先匹配类内重载
#include 特殊运算符的重载
class A {
public :
A() {
arr = new int[10];
}
A(const A &a) : A() {
//深拷贝，系统默认拷贝构造是浅拷贝()
for (int i = 0; i < 10; i++) {
this->arr[i] = a.arr[i];
}
this->x = a.x;
this->y = a.y;
}
int x, y;
int *arr;
};
class B {
public:
B() : obj(nullptr){
arr = new int[10];
arr[3] = 9972;
}
B(A *obj) : B() {
this->obj = obj;
}
int operator()(int a, int b){
return a + b;
}
int &operator[](int ind) {
//返回引用,返回的是ind处的变量
return arr[ind];
}
void operator[](const char *msg) {
cout << msg << endl;
return ;
}
A *operator->() {
return obj;
}
A &operator*() {
return *obj;
}
~B() {
delete arr;
}
private:
int *arr;
A *obj;
};
ostream &operator<<(ostream &out, const A &a) {
out << "A(" << a.x << ", " << a.y << ")";
return out;
}
//主函数中是外部表现，类中是内部实现
int main() {
B add;
cout << add(3, 5) << endl; //函数对象(像函数的对象)，重载()
add[3] = 787; //数组对象, 重载[]
cout << add[3] << endl;
add["hello world"];
A a, b(a); //浅拷贝
a.x = 87, a.y = 852;
B p = &a; //指针对象
cout << p->x << " " << p->y << endl;
cout << *p << endl;
a.arr[3] = 111;
b.arr[3] = 222;
cout << a.arr[3] << endl;
cout << b.arr[3] << endl;
cout << sizeof(a) << endl;
return 0;
}
class IntArray {
public:
IntArray(int n) : n(n) {
this->arr = new int[n];
}
IntArray(IntArray &obj) : n(obj.n){
this->arr = new int[n];
for (int i = 0; i < n; i++) {
this->arr[i] = obj[i];
}
}
int &operator[](int ind) {
if (ind >= 0) {
return this->arr[ind];
} else {
return this->arr[this->n + ind];
}
}
void operator+=(int num) {
for (int i = 0; i < n; i++) {
this->arr[i] += num;
}
return ;
}
IntArray operator++(int x) {
//后++, 无论后++还是前++都是要加的。所以要提前拷贝一份返回加之前的样子.
IntArray temp(*this);
for (int i = 0; i < this->n; i++) {
this->arr[i] += 1;
}
return temp;
}
IntArray &operator++() {
for (int i = 0; i < this->n; i++) {
this->arr[i] += 1;
}
return *this;
}
friend ostream &operator<<(ostream &, const IntArray &);
~IntArray() {
delete[] this->arr;
}
private:
int *arr, n;
};
ostream &operator<<(ostream &out, const IntArray &a) {
out << "[ ";
for (int i = 0; i < a.n; i++) {
out << a.arr[i] << " ";
}
out << "]";
return out;
}
int main() {
srand(time(0));
IntArray a(10);
for (int i = 0; i < 10; i++) {
a[i] = rand() % 100; //！！这里要注意一下如何重载[], a[i]返回值应该是arr[i]这个变量的引用
}
cout << a << endl; //输出数组中所有的元素
cout << a[4] << endl;
cout << a[-2] << endl; //输出倒数第2位的值
a += 5; //给数组的所有元素都加5
cout << a << endl; //输出数组中所有的元素
cout << (a++) << endl; //给数组中所有元素都加1
cout << (++a) << endl; //给数组中所有元素都加1
return 0;
}