c++: accessing vector elements using a pointer to the start of it

Question

I have a vector of pointers to Machines: That is,

vector<Machines*> m;

I populate the vector with pointers and I know the number of machines that exist. If I created a pointer to a pointer of Machines to the start of the vector:

Machines** m2; m2 = & m[0];

would I be accessing the vector members as I increment that '0'?

m2[0]->dostuff; m2[1]->dostuff; ...

It seems doable to me but I'm not sure if that's allowed. :)

Thank you in advance!

It's certainly legal, but seems a bit odd when you have a vector already there - side question: why a vector of pointers? Why not just a vector of Machines? — John3136
– John3136, Commented Jul 24, 2012 at 0:49
@John3136 probably Machine is a base class, in which case you need pointers to prevent slicing. — Luchian Grigore
– Luchian Grigore, Commented Jul 24, 2012 at 0:50

Jesse Good · Accepted Answer · 2012-07-24 01:00:16Z

2

It's allowed, but do you realize you can do the following and there is no reason to use Machines** m2;?

vector<Machines*> m; // Fill vector here m[0]->dostuff(); // I assumed dostuff was a function m[1]->dostuff();

answered Jul 24, 2012 at 1:00

Jesse Good

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1 Comment

Rickster Over a year ago

Oh yes I know, I was simply wondering if the above would work. I am not coding that way by any means. Thanks a lot for your answer! :)

Yuan · Accepted Answer · 2012-07-24 01:05:38Z

If reallocation of vector memory happens, the pointer in your code will be invalid.

It may happens when pushing elements to vector.

Luchian Grigore · Accepted Answer · 2012-07-24 00:49:10Z

Since vector is guaranteed to allocate continuous memory, this seems correct. But why would you? You have all this functionality directly in vector.

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