Syntax Error when using 'delete'

Question

I have a problem when using 'delete' operator. It is identified as a syntax error by VS2013 with Nov 2013 CTP compiler, giving the message: "expected a declaration". Here is the code:

int a = 1;
int* p = &a;

int* snj = new int[10];

delete p;
delete[] snj;

the `delete` shouldn't be a syntax error (assuming this code is in a function body), but it is a logical error to delete a pointer that wasn't obtained with `new`. — Sander De Dycker, Jun 05 '15 at 08:55
@RaymondChen Putting the code inside the function worked. May I ask why? P.S. Sorry, I'm just a beginner. :) — user3650284, Jun 05 '15 at 08:56
I didn't even put it in main, so code was actually not able to run anything. Thanks. — user3650284, Jun 05 '15 at 08:58

score 4 · Answer 1 · edited May 23 '17 at 12:30

4

C++ doesn't let you write arbitrary expressions in the top-level like Python or other languages. You need to place your code in a function, probably main in this case:

int main()
{
    int a = 1;
    int* p = &a;

    int* snj = new int[10];

    delete p;
    delete[] snj;
}

Note that using delete on a pointer which wasn't allocated using new is undefined behaviour.

Things like this are very basic and should be covered by your introductory book. If you don't have an introductory book, you should get one.

edited May 23 '17 at 12:30

Community

1
1

answered Jun 05 '15 at 08:57

TartanLlama

63,752
13
157
193

Whilst your answer is semantically correct, it's not valid code without a `return` statement – EdChum Jun 05 '15 at 09:05
@EdChum What do you mean? `main` has an implicit `return 0;`. – TartanLlama Jun 05 '15 at 09:06
Really, I thought you had to explicitly `return 0;` or whatever, news to me – EdChum Jun 05 '15 at 09:06
[Nope](http://stackoverflow.com/questions/22239/why-does-int-main-compile). – TartanLlama Jun 05 '15 at 09:07
OK found [this](http://stackoverflow.com/questions/4189885/why-is-explicitly-returning-0-from-main-considered-good-practice) I take it back – EdChum Jun 05 '15 at 09:07

score 0 · Answer 2 · answered Jun 05 '15 at 08:56

0

p points to the address of a. a is a local variable decalred on the stack. You can only call delete on dynalically allocated heap memory (Any variable created using the new keyword).

a is deleted automatically when it goes out of scope.

answered Jun 05 '15 at 08:56

hello_world

442
3
7

score 0 · Answer 3 · answered Jun 05 '15 at 08:57

0

You should not delete p since it is not pointing to a heap element, it points to a stack element.

answered Jun 05 '15 at 08:57

AndersK

35,813
6
60
86

Syntax Error when using 'delete'

3 Answers3