delete vs delete[]

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( POD )freeing memory : is delete[] equal to delete ?

When I was taught C++, this was a long time ago. I was told to never use delete but delete[] as performing delete[] on a single object will be equivalent to delete. Knowing not to trust teachers too much I wonder, Is this true?

Is there ever a reason to call delete instead of delete[]?

I've scanned the possibly related questions in SO, but haven't found any clear answer.

/me throws up a little. Did they recommend you always call new[1] as well? — Alex Brown, Nov 23 '10 at 11:37
Don't trust them when they tell "never". All strong statements are wrong. — Kirill V. Lyadvinsky, Nov 23 '10 at 11:45
Actually there're small range of cases where you need to use `delete[]` in C++. It is better to use `std::vector` or `boost::array`. — Kirill V. Lyadvinsky, Nov 23 '10 at 11:49
@Kirill "All strong statements are wrong." this statement is paradoxical. — Yakov Galka, Nov 23 '10 at 11:54
If use valgrind --leak-check=full ./(binary name) you will get warning "Mismatched free() / delete / delete []". It is better to compile your program with valgrind to check for memory related queries. — Santosh Sahu, Aug 13 '13 at 15:01
lol, "All strong statements are wrong", is a strong statement. — FutureSci, Oct 14 '13 at 18:21

score 117 · Accepted Answer · answered Nov 23 '10 at 11:38

From the standard (5.3.5/2) :

In the first alternative (delete object), the value of the operand of delete shall be a pointer to a non-array object or a pointer to a sub-object (1.8) representing a base class of such an object (clause 10). If not, the behavior is undefined.

In the second alternative (delete array), the value of the operand of delete shall be the pointer value which resulted from a previous array new-expression. If not, the behavior is undefined.

So no : they are in no way equivalent !

score 54 · Answer 2 · answered Nov 23 '10 at 11:39

54

delete [] is "vector delete" and corresponds to vector new, i.e. new[].

You must use the matching pair of allocators. E.g. malloc/free, new/delete, new[]/delete[], else you get undefined behavior.

answered Nov 23 '10 at 11:39

Alex Budovski

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The word "vector" in the response should be changed to "native C-style array" ? Otherwise it is just a bit confusing perhaps. – marni Oct 07 '15 at 06:03
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No, vector and scalar new/delete are well understood terms. – Alex Budovski Dec 14 '17 at 22:26

score 36 · Answer 3 · answered Nov 23 '10 at 11:38

36

No! you call delete[] when you allocate with new[], otherwise you call delete.

What teacher told you leads to undefined behaviour and, if you are lucky, an application crash.

answered Nov 23 '10 at 11:38

Simone

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score 11 · Answer 4 · edited Apr 10 '16 at 00:03

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delete is used to delete a single object, while delete[] is used to delete an array of objects. Check this link for more info.

edited Apr 10 '16 at 00:03

NmdMystery

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answered Nov 23 '10 at 11:37

jmpcm

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delete vs delete[]

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