CODEWITHSUNDEEP
c++classvector
user2290362
user2290362

Reputation: 717

Access a method of a class contained as a vector of pointers to that class

I have a vector of pointers to objects defined as:

 std::vector<queuedImage*> imgBuffer;

I pass it to the constructor of a class by reference:

processThread::processThread(std::vector<queuedImage*> &queueRef);

Within the class processThread I define:

std::vector<queuedImage*> *q;

And within the constructor I make the assignment:

q = &queueRef;

When I come to access elements of the vector which is already populated with objects, the size of the vector is as expected when accessed as:

int qSize = q->size();

Which makes me assume that this should be valid: 

q[0]->getData()

Where getData is a member of queuedImage.

However, when I compile this, it is apparently not valid as:

error: base operand of ‘->’ has non-pointer type ‘std::vector<queuedImage*>’

But when I use the . operator instead:

q[0].getData()

I get the compilation error:

error: ‘class std::vector<queuedImage*>’ has no member named ‘getData’

I think that I must be accessing the method incorrectly, but I'm not sure how to do it. Does anyone have any ideas?

Thanks!

Upvotes: 0

Views: 101

Answers (3)

πάντα ῥεῖ
πάντα ῥεῖ

Reputation: 1

Besides fixing the syntactical errors to dereference that unnecessary pointer to the vector

 (*q)[0]->getData()

you seriously should consider using smart pointers e.g. 

 std::vector<std::unique_ptr<queuedImage>>

or 

 std::vector<std::unique_ptr<queuedImage>>

to hold references in vectors, rather than raw pointers.

Which smart pointer type actually to use depends on your use case.

Upvotes: 0

ravi
ravi

Reputation: 10733

This should be

(*q)[0]->getData();

But why you are unnecessarily creating pointer to vector when you already accepted vector by reference.

Upvotes: 0

Barry
Barry

Reputation: 302807

When you're doing q[0], you're not accessing the first element of the vector, you're actually dereferencing the pointer. q[0] == *q == a vector.

What you want to do is call [0] on the vector that q is pointing to. To do that, you have to dereference q first:

(*q)[0]->getData()

Upvotes: 2

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