c++; What does the warning "enabled by default" mean during compile?

Question

My code compiles without error, but what does this mean?

 etherate.cpp:432:11: warning: deleting array ‘unsigned char broadMAC [6]’ [enabled by default]

Its from this line, where I am deleting an unsigned char array;

delete [] broadMAC;

Is it OK to leave this as it is, if not, how could I improve upon this?

Thanks.

UPDATE

How is broadMAC declared?

From about 10 lines previous;

unsigned char broadMAC[6] = {destMAC[0], destMAC[1], destMAC[2], destMAC[3], destMAC[4], destMAC[5]};

destMAC is also an unsigned char array with values stored inside it. I needed to copy them out, do something with destMAC, then restore the original values; so I have declared broadMAC and wish to delete it after.

Answer 1

broadMAC is allocated in automatic memory, like so:

unsigned char broadMAC[6];

and then you call

delete[] broadMAC;

which is wrong, since you didn't allocate it with new[].

Using delete/delete[] on memory not allocated with new/new[] results in undefined behavior, and your compiler is smart enough to tell in this case.

You needn't worry about freeing the memory, it will be freed automatically.

Answer 2

G++ allows to enable and disable many warnings (e.g. -Wctor-dtor-privacy, -Woverloaded-virtual, -W...) by specifying them on the command line. Some warnings are enabled, without the need to do so on the command line, others must be explicitly requested.

So, some warnings are:

"enabled by default"

and some are:

"disabled by default"

Answer 3

You're trying to free an array which you allocated in the stack, not heap. So when the variable becomes out of scope, it will free itself and you shouldn't/can't free it explicitly.