How to avoid big memory allocation with std::make_shared

Question

Let\'s say that I have some arbitrary class, A:

class A {
 //... stuff
};

I want to call into an external API that takes in a shared pointe

Answer 1

If you know that shared pointer you pass to foo() will not get stored, copied etc, ie will not outlive your object you can make std::shared_ptr pointed to object on the stack with empty deleter:

void emptyDeleter( A * ) {}

A a;
foo( std::shared_ptr( &a, emptyDeleter ) );

Again you need to make sure that shared pointer or it's copy will not outlive the object and well document this hack.