Iterating through a vector via pointers

Question

I'm currently writing some code that iterates through a vector and calls a simple print method for every element within that vector; however, I have very limited experience with vectors and I'm having some issues getting the compiler to accept this one particular segment of code:

std::vector<Buyer *>:: iterator it;
    Buyer *b;
    for(it = buyers->begin(); it != buyers->end(); ++it)    {
            b = *it;
            cout << b->getName();
    }

where buyers is a vector containing Buyer pointers. I'd much rather use an array for this purpose, but as I'm required to use a vector for this particular point, I'm unsure of how to iterate through it and ended up trying an iterator to get through.

The error message that springs up is:

Retailer.cpp:37:17: error: base operand of ‘->’ is not a pointer
for(it = buyers->begin(); it != buyers->end(); ++it) {
             ^
Retailer.cpp:37:40: error: base operand of ‘->’ is not a pointer
for(it = buyers->begin(); it != buyers->end(); ++it) {

From what I understand, there's apparently a pointer somewhere in that mess I'm not dereferencing, but I'm not sure which element that is or where I should dereference it... any ideas for a programmer who's had little experience with c++ vectors/iterators?

buyers is actually inherited in this class, but it's basically declared as vector<Buyer *> buyers — Vincents
– Vincents, Commented Apr 29, 2014 at 23:22
Basically declared as a vector? Can you be more specific? Your problem is most likely due to the specifics of the declaration. — MooseBoys
– MooseBoys, Commented Apr 30, 2014 at 0:54
Well, actually that's exactly how it's declared(followed by ; of course), but I believe I've fixed the problem now. Oddly enough, I seem to have solved it by simply declaring class Buyer; at the beginning of the Seller.h file. It may have to do with the fact that both are descended from the same class(which I neglected to mention), or the error simply moved to a different location in the error list - given there are still a dozen more errors in the entire project. — Vincents
– Vincents, Commented Apr 30, 2014 at 1:08

danielschemmel · Accepted Answer · 2014-04-29 23:17:00Z

3

Your error is that byuers is not a pointer, but you write buyers->begin(). This should have been a buyers.begin() instead. (The same for buyers->end() of course).

You can simplify your code significantly, if you use modern c++11:

for(Buyer* b : buyers)
{
     // do something
}

answered Apr 29, 2014 at 23:17

danielschemmel

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4 Comments

MooseBoys Over a year ago

Or even more modernly, for(auto b : buyers).

danielschemmel Over a year ago

@MooseBoys That is how I would usually do it, but I think this makes it a bit easier to understand for someone unused to c++11

Vincents Over a year ago

hmm, while I tried that, but then the error message I get reads "request for member ‘begin’ in ‘((Retailer*)this)->Retailer::<anonymous>.Seller::buyers’, which is of non-class type ‘int’ ".

danielschemmel Over a year ago

@Vincents In that case we need more context - I hardly think that you would mistake an int for an vector<Buyer*>...

nonsensickle · Accepted Answer · 2014-04-29 23:38:39Z

0

The other answers have already explained what your error is but they have not given you an answer in C++ 03, which you may be using (since I'm not sure, I'll add my own answer).

In the old C++, C++ 03, you would need to change:

for(it = buyers->begin(); it != buyers->end(); ++it)    {

to

for(it = buyers.begin(); it != buyers.end(); ++it)    {

As was already stated in the other answers, this is because the -> requires a pointer to the left of it but you don't have a pointer, you have an object so you need to use the . operator.

answered Apr 29, 2014 at 23:38

nonsensickle

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Vincents Over a year ago

Well actually I'm using c++11, but I agree the issue lies in the use of the -> operator... unfortunately switching to . doesn't really help matters, it just gives a different error message. I believe I'm losing track of what data types I'm using, so I'm going to try experimenting around with different operators until I find the right code. Thanks for the consideration, though!

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