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Answer 1

+4 A:

a NULL is a perfectly valid pointer value. If a NULL is passed in, it will be treated just like any memory address. Since you're seeing only 2 entries I would wager a guess that what you really are seeing is many NULL pointers being "added" to your set but since it is a set only one copy retained.

Edit:

To test my hypothesis of many items being added all of NULL value why not put in a simple call to cout stating "New item added with address = " the value of the pointer. Bet you'll be surprised.

wheaties 2010-01-14 21:16:16

a NULL pointer cannot be added to there, theres just no way to :o

Stranger 2010-01-14 21:18:28

Without your code I can only make the assumption you've got a container of raw pointers which do allow NULL.

wheaties 2010-01-14 21:20:05

Cannot be added? You mean I can't go `container.insert(0)`?

GMan 2010-01-14 21:22:08

It can be added theoretically, but my pointer can never be NULL (the only one place in program I insert to that set)

Stranger 2010-01-14 21:23:35

Those are famous last words: "My program can never do THAT!"

wheaties 2010-01-14 21:25:59

Stranger, are your surprised that there's a `NULL` in your container, which you didn't put there?

Dmitry 2010-01-14 21:26:19

yes, object puts itself into that set (by calling a function), null checks are also persistent.

Stranger 2010-01-14 21:29:58

Are you using the pointers "raw" or using some kind of smart pointer wrapper?

Joe 2010-01-14 21:30:35

I use raw pointers.

Stranger 2010-01-14 21:31:18

Can you please post a minimal test case that reproduces it? Or at least snippets of the code that inserts and removes and checks the container?

GMan 2010-01-14 21:32:04

I would add an assert() before the insert() to check the pointer definitely isn't NULL.

Bids 2010-01-14 21:34:35

Answer 2

+5 A:

Sets can contain pointers which can be NULL.

#include <iostream>
#include <vector>

int main () {
    std::vector<int *> foo;
    foo.push_back (NULL);
    std::cout << foo.size () << std::endl;
    return 0;
}

A container can easily contain a NULL value. Are you talking about the internals of a container getting messed up?

ezpz 2010-01-14 21:17:41

Answer 3

+1 A:

I believe a container pointer value can be set via a dereferenced non-const iterator as in (*iter) = NULL. This of course would be bad.

ergosys 2010-01-14 21:43:30

Answer 4

A:

Added source code to the paste in the main question.

Stranger 2010-01-18 20:51:03

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C++ a NULL pointer in the STL container

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