Creating and filling array dynamically

Question

I have an array which is to be filled using an object like this -

const std::map<Id, std::vector<Data>> *const DataSets[]=
{
    &object.data1,
    &object.data2,
    &object.data3,
    &object.data4
};

Condition here is, If object.data1.size() == 0 I dont want to push it into array. in that case I want to fill my array like this -

const std::map<Id, std::vector<Data>> *const DataSets[]=
{
    &object.data2,
    &object.data3,
    &object.data4
};

UPDATE I am using std::vector instead of array now and trying to initialize vector in same as array -

const std::vector<std::map<Id, std::vector<Data>>> *const DataSets
{
    &object.data1,
    &object.data2,
    &object.data3,
    &object.data4
};

I am getting error: E0146 too many initializer values. Can't I initialize my vector in this way? If not can anyone please suggest how to do that?

Thanks in advance!

Why not use std::vector instead, and push the items as needed? — Some programmer dude
– Some programmer dude, Commented May 18, 2018 at 6:33
thanks for reply @Some programmer dude since my further logic depends upon this arraya and the code is long back implemented...thatswhy not using vector. — Md. Parwez Akhtar
– Md. Parwez Akhtar, Commented May 18, 2018 at 6:36
Then there is simply no way to solve your problem. With a vector, and initializing it as soon as you have all the objects needed in in it, that's the only reasonable way to solve it in C++. If you do this in the global (or namespace) scope then another warning: Unless the objects are all defined in the same translation unit the pointers you have might not even be valid. — Some programmer dude
– Some programmer dude, Commented May 18, 2018 at 6:39
how it could be implemented if you do not know size.. also reading from vector is done in some way as from array... — Swift - Friday Pie
– Swift - Friday Pie, Commented May 18, 2018 at 6:39
Also remember that when you pass an array to a function, it naturally decays to a pointer to its first element. And you can get such a pointer from a vector as well, if you need backward compatibility. — Some programmer dude
– Some programmer dude, Commented May 18, 2018 at 6:43

Ext3h · Accepted Answer · 2018-05-18 06:34:36Z

1

You don't do that.

Respectively you don't use C style plain arrays if you want to do anything dynamic. You just wrap it in yet another std::vector because that supports dynamic sizes.

answered May 18, 2018 at 6:34

Ext3h

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3 Comments

Md. Parwez Akhtar Over a year ago

next step in my code I have a function which takes this array as one of the parameter. I cant change previous implementation but need to send data as an array...

Ext3h Over a year ago

std::vector::data() and std::vector::size() are suitable for interfacing with that legacy interface.

Md. Parwez Akhtar Over a year ago

hi @Ext3h can you please suggest solution for above? I have updated the question.

463035818_is_not_an_ai · Accepted Answer · 2018-05-18 07:21:02Z

1

[...] since my further logic depends upon this arraya and the code is long back implemented...thatswhy not using vector

Thats not a good reason for not using a vector. If you ever need a c-array you can still use std::vector::data() in combination with std::vector::size(). There is (almost) no good reason to prefer a c-array to a std::vector, even if you need c-arrays in some places.

answered May 18, 2018 at 7:21

463035818_is_not_an_ai

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