what's the difference between delete and delete[] ?

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C++

int main(int argc, char* argv[])
{
	int* p = new int[10];
	for (int i = 0; i < 12; ++i) {
		p[i] = i;
	}
	delete []p;
	return 0;
}

g++ raise an error:

"*** glibc detected *** ./a.out: free(): invalid next size (fast): 0x00000000019f9010 ***" and exit

VS2008 can not exit when delete []a, I don't know what happened in background.

I have some questions.
1. What's the difference between delete and delete[] ?
2. How does the compiler know the size of a array when using delete [] ?
3. Like the example, p has two elements overloaded, How does the compiler know the tail of p and stop deleting.

Thanks for your attention.

Posted 25-Sep-14 22:45pm

cxxxxf

Updated 25-Sep-14 23:01pm

Leo Chapiro

v2

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2 solutions

Solution 2

1. If you used new use delete, if you used new[] then use delete[].

http://stackoverflow.com/questions/4255598/delete-vs-delete[^]

2. How the compiler knows is compiler dependent.

http://stackoverflow.com/questions/975792/how-does-delete-know-the-size-of-an-array[^]

3. See above

Posted 25-Sep-14 23:26pm

User 59241

Updated 25-Sep-14 23:29pm

v4

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This content, along with any associated source code and files, is licensed under The Code Project Open License (CPOL)

Leo Chapiro · Accepted Answer · 2014-09-25T22:55:00

The error is clear, I think: just change

C++

//for (int i = 0; i < 12; ++i)

for (int i = 0; i < 10; ++i)

or change the size of array to 12.

1. The difference between delete and delete[]

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.

2, 3. How does the compiler know the size of a array when using delete [] ?
How does the compiler know the tail of p and stop deleting?

It is unspecified how the size information is stored, so each compiler may implement it in a different way, but a common way to do it is to allocate an extra block before the array. That is, when you do this:

C++

int* p = new int[10];

it actually allocates an array of 11 integers, and stores the array size in the first element

what's the difference between delete and delete[] ?

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what's the difference between delete and delete[] ?

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