Le 30/06/2014 19:20, clipka nous fit lire :
> Am 30.06.2014 18:06, schrieb Le_Forgeron:
> 
>> * "return GenericPigmentBlendMapPtr(NULL);" might compile better as
>> "return GenericPigmentBlendMapPtr()" (calling the constructor of
>> shared_ptr without argument, making a shared_ptr to nullptr.
>> (otherwise, IIRC, NULL is taken as the argument for the constructor of T
>> in shared_ptr<T>)
>>
>> (I'm more familiar with C++11 std::shared_ptr<T>, so I might be wrong
>> when applied to C++03 & boost . when I need fresh instanced value,
>> std::make_shared<T>(params for T's constructor...) is my friend)
> 
> Technically you're right in that the NULL is not required, but you're
> wrong on the details: The shared_ptr<T> constructor does /not/ pass its
> arguments to a constructor of T; in fact, it never even constructs an
> instance of T at all. Instead, it takes a /pointer/ to an
> already-created instance of T as an argument (with NULL being a valid
> parameter as well). To construct a T without make_shared (which is not
> available in TR1), you have to invoke:
> 
>     shared_ptr<T>(new T(params for T's constructor...));
> 
> As for using "return shared_ptr<T>()" instead of "return
> shared_ptr<T>(NULL)", note that those pieces of code should never be
> called in the first place anyway (they all follow either an
> "assert(false)" or an "Error(...)"), and the only reason they even exist
> is to satisfy compilers ("all control paths must return a value"). I
> prefer to go for code clarity there and leave the "NULL" parameter in.
> 

But it won't compile on gcc with NULL. :-/
(it's a reported error, not just a warning)

(as NULL is long int 0... and that's not transformable into a
shared_ptr<T>.) (nullptr seems fine for C++0x, but it's not in C++03;
does boost have it ?)

I stand corrected about the constructor syntax.

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