Dirk Gregorius wrote:
I have four easy questions regarding boost::shared_ptr:
1.) How do I pass a boost::shared_ptr to a function - via value or reference?
void ByValue( boost::shared_ptr<Foo> pFoo ); void ByReference( boost::shared_ptr<Foo>& rFooPtr );
By value when the function wants to modify its own temporary copy of the argument; by const reference or by value (slightly less efficient, but often unnoticeable) when it's an immutable input argument; by non-const reference when it's an output argument. Same as with any other "medium-weight" type.
2.) When passing a raw pointee to a function you can declare the pointee const. How do I pass a const boost::shared_ptr?
void ConstRaw( const Foo* pFoo ); void ConstSharedPtr( ??? );
shared_ptr<Foo const> pFoo
3.) Does anything speak against passing a reference to a factory function instead of returning the boost::shared_ptr?
boost::shared_ptr<Foo> Create( void ) { return boost::shared_ptr<Foo>( new Foo ); }
bool Create( boost::shared_ptr<Foo>& foo ) { // Make some validations and return false on error. // ...
// Everyting is ok. Reset the pointee and return a success foo.reset( new Foo );
return true; }
No, but you can indicate failure by returning an empty shared_ptr from the first Create. if( shared_ptr<Foo> p = Create() ) { // do something } else { // Create failed }
4.) Can I test a boost::shared_ptr against NULL like a raw pointee?
Yes, the conversion operator that enables if( p ) tests also enables p == 0 comparisons as a side effect.