高性能程序，最好是向量数组或向量载体

Question

I'm coding what has to be a high-performance program.

What I have now is an array of vectors of type "A" that I've invented. The "A" is an struct that have a long long and a double.

vector<A>* ord = new vector<A>[X];

Where X is a value that i don't know until executing time.

What I have to do is, for each vector, sort its objects by the long long variable and then perform some operations.

My question is, it's better in terms of performance what I have now `An array of vectors' or it's better to create a vector of vectors like this:

vector<vector<A>> ord;

Two thinks:

• Notice that I don't have to do operations between vectors.
• I have read in other post that it's a bad idea to use `new' operator, in this case, what I shoud use in my program.

Answer 1

A dynamically allocated array of vectors and a vector of vectors will likely be the same in optimized code. And the vector of vectors takes care of so many problems that unless you have some very unusual problem you should prefer that solution as a matter of course.

Premature optimization is the root of all evil - Sir Tony Hoare

Answer 2

You mention "X is a value that i don't know until executing time", does that mean its static?

If you need it to be dynamic use vectors, but if X doesn't change use arrays as it will save you a bit of memory (both will run at pretty much the same speed if X is static).

As for your question on when to use new, I'll defer to this post: When to use "new" and when not to, in C++?