Re: set erase of null and nonexistent elements

From:

puzzlecracker <ironsel2000@gmail.com>

Newsgroups:

comp.lang.c++

Date:

Sun, 14 Sep 2008 16:11:36 -0700 (PDT)

Message-ID:

<820668c7-ad14-48c5-b2bd-d53b8cff5d1b@z66g2000hsc.googlegroups.com>

Anyway, the code below does not make any use of operator(). It uses
std::less<A*>. If that is not specialized in A.h, the remarks below apply.
If it is specialzed, you have to make sure it is a strict total ordering.

I meant something else entirely. I was refering to algorithms, such as
find_if where passed predicate, which implemented operator () for
comparison. I assume set uses operator == to locate elements of UDT.
Correct me if am wrong.

What does standard or popular implementation dictate of the following
example:

#include<set>
#include "A.h"

using std::set

int main(int argc, char **argv)
{
     std::set<A *> aSet;
     A *nullA=0;
     A *a=new A("NOT HERE")

      set.insert(new A("something"))
     //here is the list of operations I am
     aSet.erase(nullA);

null-op: nullA is not in the set.

aSet.erase(a);

null-op: a is not in the set.

//clean up and return
return 0;
}

How do standard containers (instantiated with some pointer to user-
defined type) behave in the presence of null pointer?

Well, if we insert a null pointer into a set, wouldn't it cause an
error whenever the container would try to invoke its member.

Wait, perhaps an std container doesn't do that, hence no errors are to
be seen, then how does find work?