delete vs ::delete in c++

mar 9, 2023

Most of the time you just write:

Base* ptr = new Derived();
delete ptr;           // virtual destructor cleans up Derived as expected

delete does two things: it runs the destructor and it calls the deallocation function that matches the allocation used.

If you add the global-scope qualifier:

::delete ptr;         // forces the global operator delete

you bypass overload resolution and ask for the plain global operator delete. On GCC and Clang that means the sized-delete overload is selected with sizeof(Base), so only the base-class portion of the allocation is released. MSVC still frees the full block because it passes the real size through the destructor.

when would you ever want ::delete?

Pretty much only when you're writing allocator glue or testing something very low-level and you need to skip class-specific or placement deletes. For everyday code, stick with plain delete.

quick checklist

expression	what happens	safe
`delete ptr;`	runs dynamic destructor, calls matching deallocator	yes
`::delete ptr;`	forces global deallocator; size may be wrong on gcc/clang	no

Bottom line: use plain delete unless you have a concrete, allocator-level reason to do otherwise.