Re: Problem in deleting entries from Hash_set

Prafulla T <>
Sat, 7 Mar 2009 01:03:49 -0800 (PST)
On Mar 6, 7:58 pm, ZikO <> wrote:

Prafulla T wrote:

 > for (hash_set<UserType*>::iterator hashIt = hashSet.begin(=


 > hashIt != hashSet.end(); hashIt++)
 > {
 > UserType *pUserType = *hashIt;
 > hashIt++;
 > delete pUserType;
 > pUserType = NULL;
 > }

OK. First of all you cannot use hash_set.begin(). hash_set<> is the type
not instantiated object! If this worked, that code below would also work =


template <class T>
struct A {
    void begin() {}};

int main() {
    //! A.f(); // very baaaad :P
    A<int> a;
    a.f(); // correct


hashSet was the name of hash_set object.
It is not clear to me how it would cause the problem.
And yes, incrementing iterator twice was a problem. I think I put this
while writing the mail. it was not actually there in the code. (It was
not in "for loop" in actual code).

I debugged it further and found that cause was somewhere else.
Of course, i missed to clear the hash_set after deleting the elements.
It didn't cause any trouble in my case.

* you are trying to delete object pointed by pUserType, which has not
been created dynamically by operator new !!!

It was created dynamically by operator new. I just didn't add that
code here.

* you compare pointers of two different objects, UserType with container
hash_set !!!


Now having said that all, if I understand you, your code should look
like below (roughly):

// ...
hash_set<UserType*> hsutp; // it can be any name used by you
                            // I assume u hav=

e done something on

                            // this object !!=


// ...
for (hash_set<UserType*>::iterator hashIt = hsutp.begin();
           hashIt != hsutp.end(); ++hashIt) {
   delete *hashIt;
   *hashIt = 0;



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