Deallocation of memory

[gregarion]

Hey guys, i have 2 questions to ask. Firstly ,i would like to comfirm, does using clear()function on vector and multimap , helps to destroy the elements in the vector and deallocate memory space since the elements inside it was destroyed? If it isnt, what functions can i use to make sure memory allocated to it will be deallocated.

[savavampir]

vector::clear calls erase witch erases all elements. If you are holding pointers in your vector and used something like this:

class Foo;
...
vector<Foo*> v;
Foo* pfoo = new Foo;
v.push_back(pfoo)

you must free memory your self:

vector<Foo*>::iterator i;
for(i = v.begin(); i != v.end(); ++i)
{
    delete (*i);//delete data that was pointed
    *i = 0;
}
v.clear();

[gregarion]

so i first call each element and then delete each seperately . Then i proceed to clear the vector ?

[savavampir]

Yes but not necessary. And even better:

for(...)
{
...
}
v.clear();
v.shrink_to_fit();//this gets rid of all allocations 

But be carfull not to use pfoo pointer afterward as it points to freed memory and might crash your app!

Edit: If you can somehow gather thos "garbage" pointers, just assign them null:

vector<Foo*>::iterator i;
for(i = v.begin(); i != v.end(); ++i)
{
    delete (*i);//delete data that was pointed
    *i = 0;
}
v.clear();
v.shrink_to_fit();
...
pfoo0 = 0;
pfoo1 = 0;
pfoo2 = 0;
...

[gregarion]

How about just a normal string vector which does not contain pointers?

For example

 vector<string> HeaderVec2;
vector<string>::iterator i;

HeaderVec2.push_back("Name");
HeaderVec2.push_back("Randy");

for (i = HeaderVec2.begin(); i != HeaderVec2.end(); ++i)
{
        delete (*i);
}

HeaderVec2.clear();

When i tried doing this , i got an error " error: type ‘struct std::pair<const std::basic_string<char, std::char_traits<char>, std::allocator<char> >, int>’ argument given to ‘delete’, expected pointer ". Is this due to the fact that, i just normally inserted values into my vector without using pointers?

[savavampir]

You don't need to must not call delete if you are not created elements on the heap with new.
In this case clear() & shrink_to_fit() is enough!

class Foo;
...
Foo f;
vector<Foo> v;
v.push_back(f);
...
v.clear();
v.shrink_to_fit();

[savavampir]

If you are unsure if you got memory leaks, i highly recommend this library:
http://www.softpedia.com/get/Programming/Components-Libraries/Visual-Leak-Detector.shtml

To moderators:
I can't find home page for this version of VLD (2.1) so i provided link from softpedia.

[Galik]

As far as I know there is no way to reduce the memory allocated to a std::vector. What you can do is either create the vector using new so you can delete it when you want to return the memory or put the vector in its own scope:

int main()
{
    // do some stuff

    { // introduce a new scope

        std::vector<int> v;
        // do stuff with vector

    } // end of scope, vector is destroyed returning memory

    // do some more stuff
}