using函式指標別名
Prerequisites:
以上文章必須看完，才能往下看。
using替函式指標取類型別名
與typedef一樣，都是替函式指標取類型別名
定義函式指標類型別名語法
using 類型別名 = 函式指標
using Func = void(int, const string&);
函式宣告
print函式與void(int, const string&)是相符
注意！以下的print後面是沒有()括號
Func print;
以上程式碼等同普通函式宣告
void print(int, const string&);
函式定義
所謂的函式定義就是有實作程式碼的函式
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//Func類型別名
using Func = void(int, const string&);
//函式宣告
Func print;
int main() {
return 0;
}
//函式定義
void print(int code, const string& msg) {
cout << "Error code = " << code << " , Msg = " << msg << endl;
}
Error code = 500 , Msg = Server error.
函式指標
宣告函式指標，並指向函式
類型別名* 函式指標變數名 = 函式;
Func* func_pointer = print;
呼叫函式
函式指標變數名(參數)
func_pointer(500, "Server error.");
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//Func函式類型別名
using Func = void(int, const string&);
//函式宣告
Func print;
int main() {
//宣告函式指標，指向print函式
Func* func_pointer = print;
//呼叫函式
func_pointer(500, "Server error.");
//宣告函式參考，指向print函式
Func* func_ref = print;
func_ref(400, "Not Found.");
return 0;
}
//函式定義
void print(int code, const string& msg) {
cout << "Error code = " << code << " , Msg = " << msg << endl;
}
Error code = 400 , Msg = Not Found.
函式參考
宣告函式參考，並指向函式
類型別名& 函式指標變數名 = 函式;
Func& func_ref = print;
呼叫函式
函式參考變數名(參數)
func_ref(500, "Server error.");
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//Func函式類型別名
using Func = void(int, const string&);
//函式宣告
Func print;
int main() {
//宣告函式參考，指向print函式
Func* func_ref = print;
//呼叫函式
func_ref(400, "Not Found.");
return 0;
}
//函式定義
void print(int code, const string& msg) {
cout << "Error code = " << code << " , Msg = " << msg << endl;
}
Error code = 400 , Msg = Not Found.
類別靜態函式指標
函式指標語法
加上類別名字以及範圍運算子::
void (*func_pointer)(int, const string&) = Student::print;
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class Student {
public:
static void print(int code, const string& msg) {
cout << "Error code = " << code << " , Msg = " << msg << endl;
}
};
int main() {
//宣告函式指標
void (*func_pointer)(int, const string&) = Student::print;
func_pointer(500, "Server error.");
return 0;
}
Error code = 500 , Msg = Server error.
使用using函式指標別名
加上類別名字以及範圍運算子::
Func *func_p = Student::print;
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class Student {
public:
static void print(int code, const string& msg) {
cout << "Error code = " << code << " , Msg = " << msg << endl;
}
};
//Func函式類型別名
using Func = void(int, const string&);
int main() {
//函式類型別名宣告函式指標
Func *func_p = Student::print;
func_p(404, "Page not Found.");
return 0;
}
Error code = 404 , Msg = Page not Found.
物件成員函式指標
物件成員函式指標語法
- 必須把記憶體位址傳進去，所以有使用&取位址運算子
- 呼叫函式時，使用物件加點(.)運算子與指標運算子(*)
void(Student::* func_pointer)(int, const string&) = &Student::print; (student.*func_pointer)(500, "Server error.");
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class Student {
public:
void print(int code, const string& msg) {
cout << "Error code = " << code << " , Msg = " << msg << endl;
}
};
int main() {
//物件宣告
Student student;
//成員函式轉成函式指標
void(Student::* func_pointer)(int, const string&) = &Student::print;
//函式指標呼叫函式
(student.*func_pointer)(500, "Server error.");
return 0;
}
Error code = 500 , Msg = Server error.
使用using函式指標別名
- 函式指標類型別名
using Func = void(Student::*)(int, const string&); - 建立函式指標
Func func_pointer = &Student::print; - 呼叫函式指標
(student.*func_pointer)(400,"Page not found.");
完整程式碼
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class Student {
public:
void print(int code, const string& msg) {
cout << "Error code = " << code << " , Msg = " << msg << endl;
}
};
//Func函式類型別名
using Func = void(Student::*)(int, const string&);
int main() {
//建立物件
Student student;
//建立函式指標
Func func_pointer = &Student::print;
//呼叫函式指標
(student.*func_pointer)(400,"Page not found.");
return 0;
}
Error code = 400 , Msg = Page not found.