分享C++三种类型new类型的运算符使用详情
时间：2022-09-01 09:26:10 | 栏目：C代码 | 点击：次
1.new操作符
new operator，平时用的最多的new操作符，其对应delete operator，不能被重载，其包含两个操作（既申请空间，又调用构造函数）
- （1）使用::operator new申请内存
- （2）调用类的构造函数
class CTestUse
{
public:
CTestUse() { cout << __FUNCTION__ << endl; }
virtual ~CTestUse() { cout << __FUNCTION__ << endl; }
private:
};
void test()
{
string *pStr = new string("new operator");
cout << *pStr << endl;
delete pStr;
CTestUse *pCase = new CTestUse;
delete pCase;
}
int main(int argc, char *argv[])
{
test();
return 0;
}
运行结果如下：
2.::operator new
::operator new，只会申请空间，不会调用构造函数，可以被重载，其对应 ::operator delete （只申请空间）
2.1原始调用
class CTestUse1
{
public:
CTestUse1() { cout << __FUNCTION__ << endl; }
virtual ~CTestUse1() { cout << __FUNCTION__ << endl; }
void show() { cout << __FILE__ << " " << __FUNCTION__ << endl; }
private:
};
void test1()
{
CTestUse1 *pCase = (CTestUse1 *)::operator new (sizeof(CTestUse1));
pCase->show();
::operator delete(pCase);
}
int main(int argc, char *argv[])
{
test1();
return 0;
}
运行结果如下：
2.2重载1
class CTestUse2
{
public:
CTestUse2() { cout << __FUNCTION__ << endl; }
virtual ~CTestUse2() { cout << __FUNCTION__ << endl; }
void show() { cout << __FILE__ << " " << __FUNCTION__ << endl; }
void* operator new(size_t size) {
cout << __FUNCTION__ << endl;
return ::operator new(size);
}
void operator delete(void* ptr) {
cout << __FUNCTION__ << endl;
::operator delete(ptr);
}
private:
};
void test2()
{
CTestUse2 *pCase = new CTestUse2;
pCase->show();
delete pCase;
}
int main(int argc, char *argv[])
{
test2();
return 0;
}
运行结果如下：
2.3重载2
class CTestUse3
{
public:
CTestUse3() { cout << __FUNCTION__ << endl; }
virtual ~CTestUse3() { cout << __FUNCTION__ << endl; }
void show() { cout << __FILE__ << " " << __FUNCTION__ << endl; }
void* operator new(size_t size, string str) {
cout << __FUNCTION__ << str << endl;
return ::operator new(size);
}
void operator delete(void* ptr) {
cout << __FUNCTION__ << endl;
::operator delete(ptr);
}
private:
};
void test3()
{
CTestUse3 *pCase = new ("heshiyang") CTestUse3;
pCase->show();
delete pCase;
}
int main(int argc, char *argv[])
{
test3();
return 0;
}
运行结果如下：
3.place new
place new在已经构建好的内存中创建对象，其只会返回已经申请好的内存指针，多用在高性能场景下，提前申请好内存，可以节省申请内存开消 （只调用构造函数）
class CTestUse4
{
public:
CTestUse4() { cout << __FUNCTION__ << endl; }
virtual ~CTestUse4() { cout << __FUNCTION__ << endl; }
void show() { cout << __FILE__ << " " << __FUNCTION__ << endl; }
void* operator new(size_t size, void* p) {
cout << __FUNCTION__ << endl;
return p;
}
void operator delete(void* ptr) {
cout << __FUNCTION__ << endl;
::operator delete(ptr);
}
private:
};
void test4()
{
char* pChar = new char[sizeof(CTestUse4)];
CTestUse4* pCase = new (pChar) CTestUse4; //调用全局::new (pChar) CTestUse4，new (pChar) CTestUse4调用重载new
//delete pCase;
pCase->~CTestUse4();
}
int main(int argc, char *argv[])
{
test4();
return 0;
}
运行结果如下：
