类对象加括号与不加括号

 声明一个对象，不加括号一般调用默认构造函数

15 T t1; // is obj：Default Constructor

注意：如声明一个对象，加括号，这里一般编译器把这个当成无形参的函数，返回类型为T
18 T t2(); // is function. name is t2, return T

 声明一个对象，加括号一般调用用户定义的构造函数
21 T t3(3); // is obj. Define Constructor

 

new关键字创建对象时
对于内置类型(比如int, char):加括号会初始化，不加括号不初始化.
对于自定义类型:都会调用默认构造函数，加不加括号没区别.

 

#include <stdio.h>
#include <stdlib.h>
#include <unistd.h>

class T {
    public:
        T(){printf("Default Constructor!\n");};
        T(int a){printf("Define(%d) Constructor!\n", a);};

        ~T(){printf("Destructor!\n");};
};

int main(int argc, char *argv[])
{
    T t1;  // is obj：Default Constructor
    printf("______1st_______\n");

    T t2();  // is function. name is t2, return T
    printf("______2nd_______\n");

    T t3(3);  // is obj. Define Constructor
    printf("______3th_______\n");

    T* t4 = new T;  // is Point. DC
    printf("______4th_______\n");

    T* t5 = new T();  // is Point. DC
    printf("______5th_______\n");

    delete t4;
    delete t5;

    return (EXIT_SUCCESS);
}

输出

root@ubuntu:~/Test/test/
$ a.out

Default Constructor!
______1st_______
______2nd_______
Define(3) Constructor!
______3th_______
Default Constructor!
______4th_______
Default Constructor!
______5th_______
Destructor!
Destructor!
Destructor!
Destructor!