Popping the last item in a std::vector

[James Brown]

Hi,
I am using the std::vector class as follows:

vector <myclass *> stack1;

and am pushing myclass objects onto the end of the
vector like so:

myclass *ptr = new myclass();
stack1.push_back(ptr);

what I would like to do is pop this item from the end of
the vector as well, however the vector:op_back method does not
return anything (it has a void return-type). So my question is, what
is the preferred, neatest method to pop the last element from a vector
but also retain that value?

maybe iterators or direct-access using the operator[], followed by the
pop_back call?
Basically I'd like to know what the most common method is to do this...


Thanks,
James

 

[Rolf Magnus]

Hi,
I am using the std::vector class as follows:

vector <myclass *> stack1;

and am pushing myclass objects onto the end of the
vector like so:

myclass *ptr = new myclass();
stack1.push_back(ptr);

What about std::stack?

what I would like to do is pop this item from the end of
the vector as well, however the vector:op_back method does not
return anything (it has a void return-type). So my question is, what
is the preferred, neatest method to pop the last element from a vector
but also retain that value?

myclass* ptr = stack1.back();
stack1.pop_back();

 

[Mike Wahler]

Hi,
I am using the std::vector class as follows:

vector <myclass *> stack1;

and am pushing myclass objects onto the end of the
vector like so:

myclass *ptr = new myclass();
stack1.push_back(ptr);

what I would like to do is pop this item from the end of
the vector as well, however the vector:op_back method does not
return anything (it has a void return-type). So my question is, what
is the preferred, neatest method to pop the last element from a vector
but also retain that value?

if(!stack1.empty())
{
myclass *p = *(stack1.end()-1);
stack1.pop_back();
}

IMO 'stack1' isn't a very good name for a vector.
The standard library does have a 'stack' container,
perhaps you want to use that instead.

-Mike

 

[Victor Bazarov]

[...]
IMO 'stack1' isn't a very good name for a vector.
The standard library does have a 'stack' container,

Ahem... 'stack' container _adaptor_.

perhaps you want to use that instead.

V

 

[msalters]

Hi,
I am using the std::vector class as follows:

vector <myclass *> stack1;

and am pushing myclass objects onto the end of the
vector like so:

myclass *ptr = new myclass();
stack1.push_back(ptr);

what I would like to do is pop this item from the end of
the vector as well, however the vector:op_back method does not
return anything (it has a void return-type). So my question is, what
is the preferred, neatest method to pop the last element from a vector
but also retain that value?

There is intentionally no such method. The reason is exception-safety,
which is relevant whenever vector holds elements whose copy ctor
can throw. The bad scenario is: vector<T>:op_back copies the last
element into a temporary (OK), destroys the last object of the array
(OK, shouldn't throw), and then tries to return the temporary(THROWS).
Now the last object is lost forever. That's bad.

Your case is different, because you know pointer copies won't throw.
So you can use that specialized knowledge to implement a free function
doing exactly what I described.

Regards,
Michiel Salters

 

[msalters]

Hi,
I am using the std::vector class as follows:

vector <myclass *> stack1;

and am pushing myclass objects onto the end of the
vector like so:

myclass *ptr = new myclass();
stack1.push_back(ptr);

what I would like to do is pop this item from the end of
the vector as well, however the vector:op_back method does not
return anything (it has a void return-type). So my question is, what
is the preferred, neatest method to pop the last element from a vector
but also retain that value?

There is intentionally no such method. The reason is exception-safety,
which is relevant whenever vector holds elements whose copy ctor
can throw. The bad scenario is: vector<T>:op_back copies the last
element into a temporary (OK), destroys the last object of the array
(OK, shouldn't throw), and then tries to return the temporary(THROWS).
Now the last object is lost forever. That's bad.

Your case is different, because you know pointer copies won't throw.
So you can use that specialized knowledge to implement a free function
doing exactly what I described.

Regards,
Michiel Salters

 

[Mike Wahler]

[...]
IMO 'stack1' isn't a very good name for a vector.
The standard library does have a 'stack' container,

Ahem... 'stack' container _adaptor_.

Um, I'll try to wiggle out: 'stack' type.

You just like to pick on me, huh?

-Mike

 

[Victor Bazarov]

X-No-archive: yes

[...]
IMO 'stack1' isn't a very good name for a vector.
The standard library does have a 'stack' container,

Ahem... 'stack' container _adaptor_.

Um, I'll try to wiggle out: 'stack' type.

You just like to pick on me, huh?

Hey, I tried picking on girls, it didn't work very well, and
you were just there... So... )

 

[James Brown]

Thankyou all for your replies, in my ignorance
I failed to find the vector::back method, and wasn't aware
of the std::stack implementation....this certainly looks like the
best solution for my needs.

Thanks,
James

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