- 论坛徽章:
- 0
|
下面的代码是boost库里的shared_ptr的定义，它的拷贝构造函数和swap()
shared_ptr(shared_ptr const & r): px(r.px) // never throws
{
pn = r.pn;
++*pn;
}
void swap(shared_ptr<T> & other) // never throws
{
std::swap(px, other.px);
std::swap(pn, other.pn);
}
为什么这里是直接引用的私有的成员变量px,pn?这样能通过编译吗？还是有其他的trick在里面？
//摘自boost_1_36_0/boost/detail/shared_ptr_nmt.hpp
template<class T> class shared_ptr
{
private:
typedef detail::atomic_count count_type;
public:
typedef T element_type;
typedef T value_type;
explicit shared_ptr(T * p = 0): px(p)
{
#ifndef BOOST_NO_EXCEPTIONS
try // prevent leak if new throws
{
pn = new count_type(1);
}
catch(...)
{
boost::checked_delete(p);
throw;
}
#else
pn = new count_type(1);
if(pn == 0)
{
boost::checked_delete(p);
boost::throw_exception(std::bad_alloc());
}
#endif
}
~shared_ptr()
{
if(--*pn == 0)
{
boost::checked_delete(px);
delete pn;
}
}
shared_ptr(shared_ptr const & r): px(r.px) // never throws
{
pn = r.pn;
++*pn;
}
shared_ptr & operator=(shared_ptr const & r)
{
shared_ptr(r).swap(*this);
return *this;
}
#ifndef BOOST_NO_AUTO_PTR
explicit shared_ptr(std::auto_ptr<T> & r)
{
pn = new count_type(1); // may throw
px = r.release(); // fix: moved here to stop leak if new throws
}
shared_ptr & operator=(std::auto_ptr<T> & r)
{
shared_ptr(r).swap(*this);
return *this;
}
#endif
void reset(T * p = 0)
{
BOOST_ASSERT(p == 0 || p != px);
shared_ptr(p).swap(*this);
}
T & operator*() const // never throws
{
BOOST_ASSERT(px != 0);
return *px;
}
T * operator->() const // never throws
{
BOOST_ASSERT(px != 0);
return px;
}
T * get() const // never throws
{
return px;
}
long use_count() const // never throws
{
return *pn;
}
bool unique() const // never throws
{
return *pn == 1;
}
void swap(shared_ptr<T> & other) // never throws
{
std::swap(px, other.px);
std::swap(pn, other.pn);
}
private:
T * px; // contained pointer
count_type * pn; // ptr to reference counter
};
[ 本帖最后由 jazy333 于 2008-8-28 14:15 编辑 ] |
|
免费注册
发表于 2008-08-28 14:08
