Knowledge of C ++ in the new

In C ++, we often encounter three kinds of new forms: operator new, new operator, placement new

Operator ①new  (new new operator) : ① ② space applications create objects

Illustrates the steps of:

 

②operator new (operator new new) : Application Space

③placement new (locating new new) : create an object in space has applied

Format: new (ptr) A ( "123") ptr --- application point has a good spatial

 

Summary: ②③ is considered to be a simple operation ① Netvibes. However ②③, when the need to release the space, need to explicitly call spatial object class destructor release entity member applications.

 

Application Code:

#include<iostream>
using namespace std;


//operator new
//new operator
//placement new

//重载new operator
void* operator new(size_t sz)
{
    void* p = malloc(sz);
    return p;
}
void operator delete(void *p)
{
    free(p);
}
void operator delete[](void *p)
{
    free(p);
}

class String;
ostream& operator<<(ostream& out, String& str);

class String
{
public:
    friend ostream& operator<<(ostream& out, String& str);
public:
    String(const char* str = "")
    {
        std::cout<<"contruct Object"<<std::endl;
        if (str == NULL)
        {
            m_data = new char[1];
            m_data[0] = '\0';
        }
        else
        {
            m_data = new char[strlen(str) + 1];
            strcpy(m_data,str);
        }
    }
    ~String()
    {
        cout<<"free Object"<<endl;
        delete[]m_data;
        m_data = NULL;
    }
    
private:
    char* m_data;
};
ostream& operator<<(ostream& out, String& str)
{
    out << str.m_data;
    return out;
}


int main()
{
    String *str = new String("Hello");// new operator
    delete str;
    String *str = new String[10];
    String *ps = (String *)operator new(sizeof(String)); //operator new
    new(ps)String("Hello");  //placement new
    ps->~String();
    operator delete(ps);
    return 0;
}