Hi, I have to classes. class Car; class Limousine : public Car{ ... }; And two vector vector<Car> Cars; vector<Limousine> Limousines; I want to set vector Limousines's to vector Cars( Cars = Limousines ). One method is: vector<Limousine>::iterator pos; for ( pos = Limousines.begin() ; pos != Limousines.end() ; ++ pos ){ Car car; car = static_cast <Car>(*pos); Cars.push_back ( car ); } However, I think it is to clumsy :0 .Who can provide me with a easier method(e.g:using copy() or other std function).thx zlf
Hi, I have to classes.
class Car; class Limousine : public Car{ ... };
And two vector vector<Car> Cars; vector<Limousine> Limousines;
I want to set vector Limousines's to vector Cars( Cars = Limousines ). zlf
Since a Limousine is a Car, you should able to do Cars.insert(Cars.end(), Limousines.begin(), Limousines.end()); at least if you have a recent compiler.
On 4/26/05, Philippe Mori <philippe_mori@hotmail.com> wrote:
Since a Limousine is a Car, you should able to do
Cars.insert(Cars.end(), Limousines.begin(), Limousines.end());
at least if you have a recent compiler.
And if you don't mind slicing your objects. You can't store polymorphic types directly in std containers. -- Caleb Epstein caleb dot epstein at gmail dot com
On 26 Ebr 2005, at 19:23, Caleb Epstein wrote:
On 4/26/05, Philippe Mori <philippe_mori@hotmail.com> wrote:
Since a Limousine is a Car, you should able to do
Cars.insert(Cars.end(), Limousines.begin(), Limousines.end());
at least if you have a recent compiler.
And if you don't mind slicing your objects. You can't store polymorphic types directly in std containers.
-- Caleb Epstein caleb dot epstein at gmail dot com
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Well that's easy enough to get round, use pointers. if you are storing objects in containers, it normally is good practice to use pointers anyway because the STL passes data round by value, and not my reference / pointer, and therefore unless your objects are very lightweight and/or have copy constructors, then storing objects by value is normally a big no-no in most cases. ... One good exception to the rule here would be if you had smart pointers, obviously these objects are copied into the container, and these are lightweight and implement copy constructors / assignment operators. Generally, if you are going to use pointers, depending on the complexity of the object life-cycle, it is often wise to use something like boost::shared_ptr , as it will reduce the the risks of things like dangling pointers etc etc. Jason
On Tue, Apr 26, 2005 at 07:38:16PM +0100, Jason Earl wrote:
On 26 Ebr 2005, at 19:23, Caleb Epstein wrote:
On 4/26/05, Philippe Mori <philippe_mori@hotmail.com> wrote:
Since a Limousine is a Car, you should able to do
Cars.insert(Cars.end(), Limousines.begin(), Limousines.end());
at least if you have a recent compiler.
That might look nicer than the original, but only ...
And if you don't mind slicing your objects. You can't store polymorphic types directly in std containers.
Well that's easy enough to get round, use pointers. if you are storing objects in containers, it normally is good practice to use pointers anyway because the STL passes data round by value, and not my reference / pointer, and therefore unless your objects are very lightweight and/or have copy constructors, then storing objects by value is normally a big no-no in most cases.
I would argue that it is only good practice if your objects are polymorphic, recommending storing raw pointers as generally "good practice" is highly questionable, given the alternatives available today. Who would own the pointee if you copy a Limousine* into vector<Car*> ? Boost ptr_container is a better solution than raw pointers. Or if you want to store by value but avoid excessive copying of heavyweight objects don't use std::vector, use std::list or another container.
... One good exception to the rule here would be if you had smart pointers, obviously these objects are copied into the container, and these are lightweight and implement copy constructors / assignment operators. Generally, if you are going to use pointers, depending on the complexity of the object life-cycle, it is often wise to use something like boost::shared_ptr , as it will reduce the the risks of things like dangling pointers etc etc.
But conceptually storing a smart ptr is storing an object by pointer, the fact that the smart ptr is stored by value is a distraction, you're concerned with the pointee not the pointer. *obviously* you store the actual smart ptr by value, storing a pointer to a smart ptr in a container would be ludicrous! jon -- Rules of Optimization: Rule 1: Don't do it. Rule 2 (for experts only): Don't do it yet. - M.A. Jackson
At Tuesday 2005-04-26 11:10, Philippe Mori wrote:
Hi, I have to classes.
class Car; class Limousine : public Car{ ... };
And two vector vector<Car> Cars; vector<Limousine> Limousines;
I want to set vector Limousines's to vector Cars( Cars = Limousines ). zlf
Since a Limousine is a Car, you should able to do
Cars.insert(Cars.end(), Limousines.begin(), Limousines.end());
at least if you have a recent compiler.
the OP should note that doing this is going to "slice" each Limousine down to a Car. IF the original intent (NOT stated) was to have a single vector which held both Cars and Limousines then some other approach would be needed (such as a vector<Car*> or better, one of the smart pointers instead of the raw Car*).
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Victor A. Wagner Jr. http://rudbek.com The five most dangerous words in the English language: "There oughta be a law"
participants (2)
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Caleb Epstein -
Jason Earl -
Jonathan Wakely -
Philippe Mori -
Victor A. Wagner Jr. -
zlf