operator=()
Prerequisites:
指派運算子使用方式
二個物件都已經存在，其中一個物件指派另一個物件。
編譯器預設會有預設的指派運算子operator=()，使用者可改寫。
改寫operator=函式的語法如下
類別名& operator=(const 類別名& src來源物件);
完整程式碼
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#include <iostream>
using namespace std;
class Student {
public:
string m_name;
Student& operator=(const Student& s) {
m_name = s.m_name;
return *this;
}
};
int main() {
//建立二個物件
Student s1,s2;
s1.m_name = "Bill";
//使用operator=函式
s2 = s1;
cout << "s1 name = " << s1.m_name << endl;
cout << "s2 name = " << s2.m_name << endl;
return 0;
}
s1 name = Bill
s2 name = Bill
深拷貝
預設是淺拷貝。
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#include <iostream>
using namespace std;
class Student {
public:
string m_name;
int* m_ptr;
Student(){m_ptr = nullptr;}
~Student(){if(m_ptr) delete m_ptr;}
//參數為來源物件，也就是指要copy的物件
Student& operator=(const Student& src) {
m_name = src.m_name;
//如果來源物件的m_ptr指標是空
if(src.m_ptr == nullptr) {
//要把目的物件清空(如果目的物件不是空的話)
if(m_ptr != nullptr) {
delete m_ptr;
m_ptr = nullptr;
}
} else {
//如果目的物件為空
if(m_ptr == nullptr) {
//動態分配記憶體
m_ptr = new int;
}
//記憶體的值拷貝
memcpy(m_ptr, src.m_ptr, sizeof(int));
}
return *this;
}
};
int main() {
//建立二個物件
Student s1,s2;
s1.m_name = "Bill";
s1.m_ptr = new int(15);
//使用operator=函式
s2 = s1;
cout << "s1 name = " << s1.m_name << endl;
cout << "s2 name = " << s2.m_name << endl;
cout << "s1 m_ptr = " << *s1.m_ptr << endl;
cout << "s2 m_ptr = " << *s2.m_ptr << endl;
return 0;
}
s1 name = Bill
s2 name = Bill
s1 m_ptr = 15
s2 m_ptr = 15