派生類同樣有構造函數。當我們創建一個派生類對象的時候，基類構造函數將會被自動調用，用于初始化派生類從基類中繼承過來的成員變量。而派生類中新增的成員變量則需要重新定義構造函數用于初始化了。

#include<iostream> using namespace std;class book { public:book();book(char* a, double p = 5.0);void setprice(double a);double getprice()const;void settitle(char* a);char * gettitle()const;void display(); private:double price;char * title; };class book_derived :public book { public:book_derived(){cout<<"book_derived 構造函數"<<endl;}void display(); };book::book(char* a, double p) {title = a;price = p; }book::book() {cout<<"book 構造函數"<<endl;title = "NoTitle";price = 0.0; }void book::setprice(double a) {price = a; }double book::getprice()const {return price; }void book::settitle(char* a) {title = a; }char * book::gettitle()const {return title; }void book::display() {cout<<"book The price of "<<title<<" is $"<<price<<endl; }void book_derived::display() {cout<<"book_derived The price of "<<gettitle()<<" is $"<<getprice()<<endl; }int main() {book_derived b;b.display();return 0; } 運行結果： book 構造函數 book_derived 構造函數 book_derived The price of NoTitle is $0

創建對象時先是執行基類的構造函數，然后再是執行派生類構造函數。構造函數執行順序是按照繼承順序自頂向下執行。

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