Item 36. Class-Specific Memory Management

Item 36. Class-Specific Memory Management

在类中声明operator new 和 operator delete 成员就可以实现类自己的内存分配与管理。

class Handle {

public:

//...

void *operator new( size_t );

void operator delete( void * );

//...

};

//...

Handle *h = new Handle; // uses Handle::operator new

//...

delete h; // uses Handle::operator delete

这样对于Handle的子类需要重载operator new 和 operator delete

class MyHandle : public Handle {

//...

void *operator new( size_t );

void operator delete( void *, size_t ); // note 2nd arg

//...

};

//...

Handle *h = new MyHandle; // uses MyHandle::operator new

//...

delete h; // uses MyHandle::operator delete

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一个误解的概念：使用new和delete意味着使用heap内存

对于全局的那个operator new 和 operator delete，事实确实如此。既然operator new 和 operator

delete 都可以自定义，因此operator new 分配的内存就可以来自heap，静态分配的内存块，标准的容

器等。如下例所示：

struct rep {

enum { max = 1000 };

static rep *free; // head of freelist

static int num_used; // number of slots used

union {

char store[sizeof(Handle)];

rep *next;

};

};

static rep mem[ rep::max ]; // block of static storage

void *Handle::operator new( size_t ) {

if( rep::free ) { // if something on freelist

rep *tmp = rep::free; // take from freelist

rep::free = rep::free->next;

return tmp;

}

else if( rep::num_used < rep::max ) // if slots left

return &mem[ rep::num_used++ ]; // return unused slot

else // otherwise, we're...

throw std::bad_alloc(); // ...out of memory!

}

void Handle::operator delete( void *p ) { // add to freelist

static_cast<rep *>(p)->next = rep::free;

rep::free = static_cast<rep *>(p);

}