CODEWITHSUNDEEP
c++
Omar Zeidan
Omar Zeidan

Reputation: 27

Vector push_back: doesn't convert parameter

Well, what I'm trying to do is to push back an object of the class I called Block onto different vectors that keep Block elements and are saved in a vector themselves.

std::vector<std::vector<Block>> mapvec;
mapvec[xcnt].push_back(new Block(xcnt,ycnt));

This is my progress until now.

error C2664: 'std::vector<_Ty>::push_back': convetion of the parameter 'Block *' in 'const Block &' not possible

(translated from German)

What should I do? Is there any other way to do what I want? Without using arrays?

Upvotes: 2

Views: 327

Answers (4)

fatihk
fatihk

Reputation: 7919

You should :

mapvec[xcnt].push_back(Block(xcnt,ycnt));

Because you are holding instances of Block's, not their pointers

Upvotes: 0

Excelcius
Excelcius

Reputation: 1690

new returns a pointer to a dynamically allocated object. This is not what you want to do here. Usually you want to pass a temporary (or already existing) object to push_back and it will insert a copy into the memory.

So, simply get rid of new. Like so:

std::vector<std::vector<Block>> mapvec;
mapvec[xcnt].push_back(Block(xcnt,ycnt));

This will make a temporary Block-object and insert a copy into the vector.

If you want to use new you need to store pointers in the vector, not Block-objects. The safest way to do this is to use smart pointers:

std::vector<std::vector<std::unique_ptr<Block>>> mapvec;
mapvec[xcnt].push_back(std::unique_ptr<Block>(new Block(xcnt, ycnt)));

That way, the memory allocated with new will be freed using delete as soon as you remove the item from the vector or the vector gets destroyed.

Upvotes: 2

stardust
stardust

Reputation: 5988

new Block(xcnt,ycnt)

gives you Block* pointing to the newly allocated Block. And your vector expects Block not Block*

Change it to

mapvec[xcnt].push_back(Block(xcnt,ycnt));

This will copy your Block in to the vector so Block class should have an accessible copy constructor.

Upvotes: 1

HonkyTonk
HonkyTonk

Reputation: 2019

Define your mapvec as

std::vector<std::vector<Block*>> mapvec;

instead?

Upvotes: 1

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