Difference between delete[i] array and delete array[i]

Question

I actually want to describe my problem first. In my code I've a base class with name Employee then I've 4 more classes. I wanted to make my class abstract (basically i was using polymorphism concept). I made a pointer array with type of base class and add objects in it(unnamed objects on heap). Now i wanted to deallocate objects. I used delete[i] array and delete array[i] both were working(one at a time). Can someone please explain the difference between both of them? Why both were working if delete[i] is wrong? I was using delete[i] array or delete array[i] with for loop.

main is like:

Employee *arr[10];
arr[0] =new SalariedEmployee ("first name","last name","number",200);

now i want to delete this object

delete[i] array seems invalid, you probably mean delete[] array; — Jarod42
– Jarod42, Commented May 21, 2020 at 8:37
"I actually want to describe my problem first" But code is more accurate. — Jarod42
– Jarod42, Commented May 21, 2020 at 8:38
No, i was not using dynamic array. My array was of fixed size 10. I was talking about deallocating objects :) — asad ullah shahid
– asad ullah shahid, Commented May 21, 2020 at 8:40

Lukas-T · Accepted Answer · 2020-05-21 09:02:23Z

3

delete[i] array;

is wrong in standard C++. But it acutally compiles on msvc (demo). It's a compiler specific extension (thanks to Blastfurnace for pointing this out).

The correct version is

delete array[i];

to destroy an object that was allocated on the heap and free the corresponding memory.

However, manual memory management can become quite hard sometimes. So the solution in modern C++ would be something like

std::array<std::uniqe_ptr<Employee>, 10> array;

for a fixed size array with pointers to Employee's.

edited May 21, 2020 at 9:02

answered May 21, 2020 at 8:54

Lukas-T

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5 Comments

Blastfurnace Over a year ago

If you add the /W4 compiler option it shows "warning C4208: nonstandard extension used: delete [exp] - exp evaluated but ignored". It's a non-conforming extension.

Blastfurnace Over a year ago

If you disable language extensions with /Za it shows "error C2203: delete operator cannot specify bounds for an array".

Konrad Rudolph Over a year ago

@Blastfurnace /Za is soft-deprecated for C++ because it has numerous bugs. Don’t use it, use /permissive- instead.

Blastfurnace Over a year ago

@KonradRudolph Thanks, that's good to know (I see the note on the MSDN page about it). Unfortunately /permissive- doesn't emit an error for this :(

Konrad Rudolph Over a year ago

@Blastfurnace Well that sucks.

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