C++从入门到精通——new和delete使用

malloc 与 new 区别

1. malloc与free 属于库函数new和delete 属于运算符
2. malloc不会调用构造函数 new 会调用构造函数
3. malloc 返回void * ，c++之下需要进行 强制转换，new 返回创建对象的指针

#include <iostream>
#include <string>
using namespace std;
class Person{
public:
  Person(){
    cout<<"构造函数调用"<<endl;
  }
  Person(int a){
    cout<<"有参构造函数调用"<<endl;
  }
  ~Person(){
    cout<<"Person析构函数调用"<<endl;
  }
};
void test01(){
  Person * p = new Person;
  delete p;
}
int main(){
  test01();
  system("pause");
  return EXIT_SUCCESS;
}

利用malloc申请

#include <iostream>
#include <string>
using namespace std;
class Person{
public:
  Person(){
    cout<<"构造函数调用"<<endl;
  }
  Person(int a){
    cout<<"有参构造函数调用"<<endl;
  }
  ~Person(){
    cout<<"Person析构函数调用"<<endl;
  }
};
void test01(){
  Person *p = (Person *)malloc(sizeof(Person));

  free(p);
}
int main(){
  test01();
//  system("pause");
  return EXIT_SUCCESS;
}

不要用void 接受new出来的对象，利用void无法调用析构函数

#include <iostream>
#include <string>
using namespace std;
class Person{
public:
  Person(){
    cout<<"构造函数调用"<<endl;
  }
  Person(int a){
    cout<<"有参构造函数调用"<<endl;
  }
  ~Person(){
    cout<<"Person析构函数调用"<<endl;
  }
};
void test01(){
  void *p = new Person;
  delete p;
}
int main(){
  test01();
//  system("pause");
  return EXIT_SUCCESS;
}

利用new开辟数组，一定调用默认构造函数

#include <iostream>
#include <string>
using namespace std;
class Person{
public:
  Person(){
    cout<<"构造函数调用"<<endl;
  }
  Person(int a){
    cout<<"有参构造函数调用"<<endl;
  }
  ~Person(){
    cout<<"Person析构函数调用"<<endl;
  }
};
void test01(){
  // 堆区开辟数组，一定调用默认构造函数
  Person *pPerson = new Person[10];
  delete []  pPerson;
}
int main(){
  test01();
//  system("pause");
  return EXIT_SUCCESS;
}

#include <iostream>
#include <string>
using namespace std;
class Person{
public:
  Person(){
    cout<<"构造函数调用"<<endl;
  }
  Person(int a){
    cout<<"有参构造函数调用"<<endl;
  }
  ~Person(){
    cout<<"Person析构函数调用"<<endl;
  }
};
void test01(){
  // 堆区开辟数组，一定调用默认构造函数
  Person pArray[10] = {
      Person(10),
      Person(20),
      Person(20),
      Person(20)
  };
}
int main(){
  test01();
//  system("pause");
  return EXIT_SUCCESS;
}