CODEWITHSUNDEEP
c++vectorstruct
thenoGk
thenoGk

Reputation: 33

Working with structure objects

I have a logic that looks like the below (Not the actual code):

StructureElement x;

For i in 1 to 1000

do
    x.Elem1 = 20;
    x.Elem2 = 30;
    push(x into a std::vector)   
end

My knowledge is that x be allocated memory only once and that the existing values will be overwritten for every iteration. Also, the 'x' pushed into the vector will not be affected by subsequent iterations of pushing a modified 'x'.

Am I right in my observations?

Is the above optimal? I would want to keep memory consumption minimal and would not prefer using new. Am I missing anything by not using new?

Also, I pass this vector and recieve a reference to it it another method.

And, if I were to read the vector elements back, is this right?

Structure element xx = mYvector.begin()
print xx.Elem1
print xx.Elem2

Any optimizations or different ideas would be welcome.

Upvotes: 1

Views: 54

Answers (1)

juanchopanza
juanchopanza

Reputation: 227370

Am I right in my observations?

Yes, if the vector is std::vector<StructureElement>, in which case it keeps its own copies if what is pushed in.

Is the above optimal?

It is sub-optimal because it results in many re-allocations of the vector's underlying data buffer, plus unnecessary assignments and copies. The compiler may optimize some of the assignments and copies away, but there is no reason, for example, to re-set the elements of x in the loop.

You can simplify it like this:

std:vector<StructureElement> v(1000, StructureElement{20, 30});

This creates a size-1000 vector containing copies of StructureElement with the desired values, which is what you seem to be trying in your pseudo-code.

To read the elements back, you have options. A range based for-loop if you want to iterate over all elements:

for (const auto& e: v):
  std::cout << e.Elem1 << " " << e.Elem2 << std::endl;

Using iterators,

for (auto it = begin(v); it != end(v); ++it)
   std::cout << it->Elem1 << it->Elem2 << std::endl;

Or, pass ranges in to algorithms

std::transform(begin(v), end(v), ....);

Upvotes: 3

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