Is it safe to `delete this`?

c++ runtime-error self-destruction
Cristián Romo picture Cristián Romo · Feb 15, 2009 · Viewed 27.3k times · Source

In my initial basic tests it is perfectly safe to do so. However, it has struck me that attempting to manipulate this later in a function that deletes this could be a runtime error. Is this true, and is it normally safe to delete this? or are there only certain cases wherein it is safe?

Answer

Chris Peterson picture Chris Peterson · Feb 15, 2009

delete this is legal and does what you would expect: it calls your class's destructor and free the underlying memory. After delete this returns, your this pointer value does not change, so it is now a dangling pointer that should not be dereferenced. That includes implicit dereferencing using the class's member variables.

It is usually found in reference-counted classes that, when the ref-count is decremented to 0, the DecrementRefCount()/Release()/whatever member function calls delete this.

delete this is typically considered very bad form for many reasons. It is easy to accidentally access member variables after delete this. Caller code might not realize your object has self-destructed.

Also, delete this is a "code smell" that your code might not have a symmetric strategy for object ownership (who allocates and who deletes). An object could not have allocated itself with new, so calling delete this means that class A is allocating an object, but class B is later freeing it[self].

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