Re: Adding pointer to container
Kai-Uwe Bux <jkherciueh@gmx.net> kirjutas:
Paavo Helde wrote:
rpbg123@yahoo.com (Roland Pibinger) kirjutas:
On Wed, 11 Jun 2008 03:36:07 -0700 (PDT), tech rote:
Hi, i have a std::vector of pointers to base classes say
std::vector<element*> m_elements;
how do i make the followin exception safe
function()
{
element* e= new DerivedElement;
m_elements.push_back(element);
}
You question includes more than one aspect:
1. STL is designend for values only (a.k.a. 'value semantics'), not
objects or pointers to objects. Put simply, STL doesn't work with
pointers.
It seems this is so ridiculous no one has bothered to answer. For
innocent bystanders I just remind that pointers are values in C++.
It is true, though, that pointers often require special handling when
dealing with containers. The most basic issue is illustrated by
std::map< char const *, some_type >
By default, the map will compare pointer values and not the strings
they represent. Very likely that is _not_ the desired behavior.
If you specify the map keys as pointers, they will be compared as
pointers, that's it. I see nothing specific to STL here.
You could easily instruct the map to use the string comparison (if/when
needed) instead by providing an extra template argument for the map
declaration.
IOW, STL does what it is told to do. It does not attempt to read your
mind. This is a Good Thing IMO.
Regards
Paavo
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