On Sat, May 28, 2011 at 10:36:47PM -0400, Sid Sacek wrote:
This might be a unimportant question and may have already been answered many times before, but I was wondering about functions that take shared pointers as arguments. Is there ever a reason I would not want to use a shared_ptr reference as an argument? I can't think of any, but is there any?
class XYZ;
void foo( shared_ptr< XYZ > &xyz ) { }
Concurrent access to different shared_ptr instances in the same family (sourced from the same source) is safe. Concurrent access to a single shared_ptr instance is generally unsafe. Passing the shared_ptr by reference puts the onus on you to ensure that the shared_ptr instance you pass in is valid for the duration of the function call, which is non-trivial in general. Examples of the above would be foo(some_global_ptr); or foo(bar->baz); where some_global_ptr is destroyed somewhere deep in the call chain, or bar is destroyed during the call sequence. I've had real-life bugs of this kind. It's not pretty. Unless you have a genuine reason to access the same instance, try to avoid passing it by reference-to-non-const. If you feel you need to avoid the non-free copying cost, pass it by reference-to-const. -- Lars Viklund | zao@acc.umu.se