c++笔记——explicit关键字-526互联

前言：

explicit是为了自定义类在初始化或赋值时，发生数据类型隐性强制转换为类类型。

特点：

1、只对单实参的构造函数有效

2、只能在类内声明构造函数是用explict，在类外定义时不写explicit

3、explicit的构造函数在生成对象时，只能用直接初始化，不能赋值

示例1：

class Test{
public:
    //explicit Test(int a);
    Test(int a);
    Test(string str);
    ~Test()= default;

    int size_;
    string str_;

};

/*  //explicit在类外定义构造函数时，会报错
explicit Test::Test(int a){
    cout << "hello, this is testing..." << endl;
    size_ = a;
}
*/

Test::Test(int a){
    size_ = a;
    cout << "now test size." << endl;
}

Test::Test(string str) {
    str_ = str;
    cout << "now test str." << endl;
}


int main(){
    Test t0(12);//直接初始化
    Test t1 = 10;//赋值，实际上进行了隐式转换，将int型转换为Test类型
    Test t2('c');//调用的是int 字符c对应的assic码
    Test t3("jelly");//调用的是string

    return 0;
}

示例2：加上explicit

#include<iostream>
#include<vector>
#include <string>
using namespace std;


class Test{
public:
    explicit Test(int a);
    //Test(int a);
    Test(string str);
    ~Test()= default;

    int size_;
    string str_;

};

/*  //explicit在类外定义构造函数时，会报错
explicit Test::Test(int a){
    cout << "hello, this is testing..." << endl;
    size_ = a;
}
*/

Test::Test(int a){
    size_ = a;
    cout << "now test size. and size_ = " << size_ << endl;
}

Test::Test(string str) {
    str_ = str;
    cout << "now test str." << endl;
}


int main(){
    Test t0(12);
    Test t12(2.3);
    //Test t1 = 10;
    Test t2('c');
    Test t3("jelly");

    return 0;
}