My favourite C++ footgun
source link: https://dustri.org/b/my-favourite-c-footgun.html
Go to the source link to view the article. You can view the picture content, updated content and better typesetting reading experience. If the link is broken, please click the button below to view the snapshot at that time.
Artificial truth
Social media have made people way too comfortable being direspectuful and not getting punched in the face for that.
[archives] [latest] | [homepage] | [atom/rss/twitter]I'm currently learning C++ to be able to do meaningful contributions to OpenMW, so I've been reading a lot of code, and a couple of books on the topic.
But it's in Effective C++, by Scott Meyers, Item 17, that I found the most amazing trigger-happy footgun example:
processWidget(std::shared_ptr<Widget>(new Widget), priority());
std::shared_ptr is a
reference counting
implementation: it will automatically destroy the object it owns when there is
no more std::shared_ptr owning it.
Yet this code can result in a memory leak.
At first, I thought about a weird interaction between std::shared_ptr and
new, when the constructor of Widget fails, but this case is handled
by the C++ runtime.
The first trick here is that function parameters evaluation order is unspecified,
meaning that new Widget might be called, then priority(), then the value
returned by new Widget is passed to std::shared_ptr<Widget>(…).
The second one is there since this is C++, priority() might raise an exception,
meaning that new Widget will be called, but never passed to
std::shared_ptr, and thus never deleted!
As AnyOldName3 added after reading this
blogpost, this might be why there is std::make_shared,
with std::make_shared<Widget>() being kinda equivalent to std::shared_ptr<Widget>(new Widget).
Recommend
About Joyk
Aggregate valuable and interesting links.
Joyk means Joy of geeK