- 去修改调用函数的局部变量
-
对于传递比较大的参数时
1
2
3
4
5
6
7
8
9
10
11
12
13
14class Employee {
private:
string name;
string desig;
};
void (Employee emp) {
cout<<emp.getName();
cout<<emp.getDesig();
// Print more attributes
}每次调用printEmDetails时，都会创建一个Employee
-
为了防止对象切割（Object Slicing）
多态的实现是靠指针和引用，而对象的转换只能造成对象切割，不能实现多态1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28#include <iostream>
#include<string>
using namespace std;
class Pet {
public:
virtual string getDescription() const {
return "This is Pet class";
}
};
class Dog : public Pet {
public:
virtual string getDescription() const {
return "This is Dog class";
}
};
void describe(Pet p) { // Slices the derived class object
cout<<p.getDescription()<<endl;
}
int main() {
Dog d;
describe(d);
return 0;
}Output:
1
This is Pet Class
修改后
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28#include <iostream>
#include<string>
using namespace std;
class Pet {
public:
virtual string getDescription() const {
return "This is Pet class";
}
};
class Dog : public Pet {
public:
virtual string getDescription() const {
return "This is Dog class";
}
};
void describe(const Pet &p) { // Doesn't slice the derived class object.
cout<<p.getDescription()<<endl;
}
int main() {
Dog d;
describe(d);
return 0;
}Output:
1
This is Dog Class
-
为了实现函数的运行时多态
近期评论