Question

I really need some help… I detail my problem, I need an array of a certain type, but I don’t know its length before having retrieving values from other arrays, using for structures. In fact, I don’t want to spend time passing again the several loops, and i wonder the best way to do this. Should I use a stack and a counter, and after filling it, instanciate and fill the array ?

RelAttr *tab;
//need to initialize it but how
/*several for loops retrieving values*/
   tab[i] = value;
/*end for loops*/

Obviously this code is incomplete, but it is how stuff is done. And i know i can’t do the affectation without having specified the array length before…

Thanks for your help

Answer 1

Just use a std::vector.

std::vector<RelAttr> vec;

vec.push_back(a);
vec.push_back(b);
...

It manages its own growth transparently. Every time it grows, all the items are copied, but the amortized cost of this is O(1).

The storage is also guaranteed to be contiguous, so if you really need a raw C-style array, then you can simply do this:

const RelAttr *p = &vec[0];

However, you should really only do this if you have a legacy C API that you need to satisfy.