unique_ptr 提升等效吗?
boost 库中是否有 C++1x 的 std::unique_ptr 等价类?我正在寻找的行为是能够拥有异常安全的工厂函数,就像这样......
Is there some equivalent class for C++1x's std::unique_ptr in the boost libraries? The behavior I'm looking for is being able to have an exception-safe factory function, like so...
std::unique_ptr<Base> create_base()
{
return std::unique_ptr<Base>(new Derived);
}
void some_other_function()
{
std::unique_ptr<Base> b = create_base();
// Do some stuff with b that may or may not throw an exception...
// Now b is destructed automagically.
}
现在,我正在使用这个 hack,这似乎是我目前所能得到的最好的......
Right now, I'm using this hack, which seems like the best I can get at this point...
Base* create_base()
{
return new Derived;
}
void some_other_function()
{
boost::scoped_ptr<Base> b = create_base();
// Do some stuff with b that may or may not throw an exception...
// Now b is deleted automagically.
}
推荐答案
如果没有 C++0x,就不可能创建像 unique_ptr
这样的东西(它是标准库的一部分,所以 Boost 不不需要提供).
It's not possible to create something like unique_ptr
without C++0x (where it's part of the standard library, and so Boost doesn't need to provide it).
特别是如果没有右值引用(C++0x 中的一个特性),unique_ptr
的健壮实现是不可能的,无论有没有 Boost.
Specifically without rvalue references, which are a feature in C++0x, a robust implementation of unique_ptr
is impossible, with or without Boost.
在 C++03 中,有几种可能的替代方案,尽管每种方案都有其缺陷.
In C++03, there are a few possible alternatives, although each have their flaws.
boost::shared_ptr
可能是功能方面最简单的替代品.你可以安全地在任何地方使用它,否则它会使用unique_ptr
并且它会工作.由于添加了引用计数,它的效率不会那么高.但是,如果您正在寻找能够处理unique_ptr
可以做的所有事情的简单的替代品,这可能是您最好的选择.(当然,shared_ptr
也可以做更多的事情,但它也可以简单地用作unique_ptr
的替代品.)boost::scoped_ptr
与unique_ptr
类似,但不允许转让所有权.只要智能指针旨在在其整个生命周期内保持独占所有权,它就可以很好地工作.std::auto_ptr
的工作原理与unique_ptr
非常相似,但有一些限制,主要是它不能存储在标准库容器中.如果您只是在寻找一个允许所有权转移的指针,但并不打算将其存储在容器中或四处复制,那么这可能是一个不错的选择.
boost::shared_ptr
is probably the simplest replacement in terms of capabilites. You can safely use it anywhere you'd otherwise use aunique_ptr
and it'd work. It just wouldn't be as efficient, because of the added reference counting. But if you're looking for a simple drop-in replacement that's able to handle everythingunique_ptr
can do, this is probably your best bet. (Of course, ashared_ptr
can do a lot more as well, but it can also simply be used as a drop-in replacement forunique_ptr
.)boost::scoped_ptr
is similar tounique_ptr
but does not allow transfer of ownership. It works great as long as the smart pointer is meant to retain exclusive ownership throughout its lifetime.std::auto_ptr
works very similar tounique_ptr
, but has a few limitations, mainly that it can not be stored in standard library containers. If you're simply looking for a pointer that allows transfer of ownership, but which is not meant to be stored in containers or copied around, this is probably a good bet.
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