Wednesday, September 19, 2018

The delete operator rant

I have seen many instances using below code (assuming older standard before nullptr).

if (myAllocatedObject != NULL)
    delete  myAllocatedObject;

This is absolutely ridiculous. C++ standard guarantees that delete on NULL pointer is harmless and has no effect. Of-course, this is true only if object was allocated using new. It would be bad coding too if you try to deallocate memory using delete which was not constructed by new. This in fact applies to every allocator/deallocator combination.

Suppose if you use your own allocator, then the deallocator also needs to be supplied. It will be absurd if you restrict only to allocator.

Conclusively, the redundant NULL check is worthless. Also the code looks downright ugly.

How does libstdc++ behave?

While peeking  source tree, you get from

operator delete(void* ptr) _GLIBCXX_USE_NOEXCEPT

And std::free leads to cstdlib.h which in turn includes glibc stdlib.h and then to

__libc_free (void *mem)

if (mem == 0)                              /* free(0) has no effect */

Phew! We landed and also freed safely :-)

PS: I heard few static analyzers also complain if you don't wrap the delete with NULL check. I cannot vouch for this statement as of now since there was never an instance stumbled upon.

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