Getting to grips with boost::shared_ptr
Hi there, I have a class called Sounds which creates a number of Sound objects in its constructor and adds them to a local std:map variable. I also define an enum in this class which I use as the key with respect to the map. This class therefore acts as a look-up for all the sounds I wish to use. I also have a Player class which has a Play(Sound&) function. This function stops the currently playing sound and plays the new sound supplied by the argument. I also have a Stop() function which stops the current sound. I use a Sound* local variable to keep track of the current sound. The question is, how do I know that I shouldn't be using a shared_ptr instead of this pointer? - a design change which would also require storing shared_pts in the map previously mentioned. For example, I can crash my program by deleting my Sounds object before calling Player.Stop(). Using shared_ptrs would avoid this crash. However, this is a reckless way of producing a crash, are there more innocent ways in which it could occur for my Player class? For me, it feels that my Player class does not take ownership of a sound object; it simply keeps track of it and therefore I use a simple pointer. Is this the correct mentality with regard to whether I should be using a shared_ptr or a simple pointer? Thanks very much for your help, Barry
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Barry
3/24/2010 6:32:59 PM
comp.lang.c++
49423 articles. 
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* Barry: > Hi there, > > I have a class called Sounds which creates a number of Sound objects > in its constructor and adds them to a local std:map variable. I also > define an enum in this class which I use as the key with respect to > the map. This class therefore acts as a look-up for all the sounds I > wish to use. > > I also have a Player class which has a Play(Sound&) function. This > function stops the currently playing sound and plays the new sound > supplied by the argument. I also have a Stop() function which stops > the current sound. I use a Sound* local variable to keep track of the > current sound. > > The question is, how do I know that I shouldn't be using a shared_ptr > instead of this pointer? - a design change which would also require > storing shared_pts in the map previously mentioned. For example, I can > crash my program by deleting my Sounds object before calling > Player.Stop(). Using shared_ptrs would avoid this crash. However, this > is a reckless way of producing a crash, are there more innocent ways > in which it could occur for my Player class? > > For me, it feels that my Player class does not take ownership of a > sound object; it simply keeps track of it and therefore I use a simple > pointer. Is this the correct mentality with regard to whether I should > be using a shared_ptr or a simple pointer? It's OK. Consider that the same problems that you envision exist with nearly all kinds of objects in C++. To avoid the /possibility/ of dangling pointers every object would have to be allocated dynamically and managed through smart pointers and/or garbage collection. If that is what one wants then some other language, e.g. Java or C#, is a more practical answer -- it's not the C++ way. Cheers, - Alf
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Alf
3/25/2010 9:36:48 AM
Barry <bg_ie@yahoo.com> wrote in news:efac0ea9-d335-42da-8b92- cf773ad3718e@q23g2000yqd.googlegroups.com: > Hi there, > > I have a class called Sounds which creates a number of Sound objects > in its constructor and adds them to a local std:map variable. I also > define an enum in this class which I use as the key with respect to > the map. This class therefore acts as a look-up for all the sounds I > wish to use. > > I also have a Player class which has a Play(Sound&) function. This > function stops the currently playing sound and plays the new sound > supplied by the argument. I also have a Stop() function which stops > the current sound. I use a Sound* local variable to keep track of the > current sound. > > The question is, how do I know that I shouldn't be using a shared_ptr > instead of this pointer? - a design change which would also require > storing shared_pts in the map previously mentioned. For example, I can > crash my program by deleting my Sounds object before calling > Player.Stop(). Using shared_ptrs would avoid this crash. However, this > is a reckless way of producing a crash, are there more innocent ways > in which it could occur for my Player class? > > For me, it feels that my Player class does not take ownership of a > sound object; it simply keeps track of it and therefore I use a simple > pointer. Is this the correct mentality with regard to whether I should > be using a shared_ptr or a simple pointer? Yes, the only thing shared_ptr does is to keep the object alive until it is not needed any more. If you are not deleting any Sound anyway before the end of the program, then you do not need shared_ptr. OTOH if you foresee that you might want sometimes to delete a Sound in the middle of the program, for example by replacing it with an updated version loaded from disk, then shared_ptr would probably be the simplest way to achieve this feature. cheers Paavo
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Paavo
3/26/2010 7:54:30 AM
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