无法使用 `std::make_shared` 分配指针

Question

I have some trouble understanding what is the difference in terms of creating a new object of an abstract class using std::make_shared and std::shared_ptr ? So in my specific case, I am not able to use this:

p_network_connection_ = std::make_shared<awsiotsdk::NetworkConnection> (awsiotsdk::ConfigCommon::endpoint_);

But able to do this:

p_network_connection_ = std::shared_ptr<awsiotsdk::NetworkConnection>(new awsiotsdk::network::WebSocketConnection(awsiotsdk::ConfigCommon::endpoint_);

How come? As if I try the first method (using std::make_shared ), I get this error:

 error: invalid new-expression of abstract class type ‘awsiotsdk::NetworkConnection’
  { ::new((void *)__p) _Up(std::forward<_Args>(__args)...); }

Answer 1

Uhm it looks like you are creating instances of different classes. In your first example, you attempt to create an instance of awsiotsdk::NetworkConnection class. Given the error, I can assume that it is an abstract class - and thus an instance of this can not be created. In your second example you are creating an instance of new awsiotsdk::network::WebSocketConnection class. Given that it 'works' for you - it is not an abstruct class:)

So why not to try:

p_network_connection_ = std::make_shared<awsiotsdk::network::WebSocketConnection> (awsiotsdk::ConfigCommon::endpoint_);