this
this是記憶體位址
在類別的每一個成員函式，都有一個隱藏參數為this指標，this指標為「呼叫物件」的記憶體位址。
什麼是「呼叫物件」，以下例的程式範例來說，建立s1物件Student s1;，s1物件呼叫getAddressByPoint()成員函式，那麼函式中的隱藏參數this指標就是s1的記憶體位址，s1就是「呼叫物件」，也就是誰呼叫了成員函式getAddressByPoint()，this指標就是誰。
this記憶體位址存放的值就是呼叫函式的物件，也就是s1。
指標就是記憶體位址，所以函式傳回值為指標，就可以直接傳回this。
若函式傳回值為參考，就要把this指標，透過*取值運算子，取出物件，並將物件傳回。
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
class Student{
public:
// 傳回值為指標
Student* getAddressByPoint(){
return this;
}
// 傳回值為參考
Student& getAddressByRef(){
// 透過取值運算子，取出物件
return *this;
}
void func() {
cout << "call func()" << endl;
}
};
int main() {
Student s1;
Student* ptr = s1.getAddressByPoint();
cout << "address = " << ptr << endl;
ptr->func();
Student& ref = s1.getAddressByRef();
ref.func();
return 0;
}
address = 0x7ff7bfeff2e8
call func()
call func()
this指標取得物件成員變數
使用this指標取得物件成員變數要用->(箭頭)取得，因為this是指標，指向物件存放的位址。
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
class Student{
public:
string name;
Student* getAddressByPoint(){
return this;
}
Student& getAddressByRef(){
return *this;
}
void func() {
cout << "call func() name = " << this->name << endl;
}
};
int main() {
Student s1;
s1.name = "Cici";
Student* ptr = s1.getAddressByPoint();
cout << "address = " << ptr << endl;
ptr->func();
Student& ref = s1.getAddressByRef();
ref.func();
return 0;
}
address = 0x7ff7bfeff2d0
call func() name = Cici
call func() name = Cici
this比較
程式碼中的this是指呼叫函式的物件。
s1.compare(s2)這段程式碼而言，this就是s1。
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
29
30
31
class Student{
public:
Student();
~Student();
Student* getAddress(){
return this;
}
int getWeight() {
return this->weight;
}
void setWeight(int weight) {
this->weight = weight;
}
int compare(Student& s) {
return this->weight > s.weight;
}
private:
int weight;
};
int main() {
Student s1;
s1.setWeight(50);
Student s2;
s2.setWeight(45);
if(s1.compare(s2)) {
cout << "s1比較重 " << endl;
} else {
cout << "s2比較重 " << endl;
}
return;
}