https://gcc.gnu.org/bugzilla/show_bug.cgi?id=71181
Bug ID: 71181
Summary: Reserving in unordered_map doesn't reserve enough
Product: gcc
Version: 5.1.0
Status: UNCONFIRMED
Severity: normal
Priority: P3
Component: libstdc++
Assignee: unassigned at gcc dot gnu.org
Reporter: riad93 at mail dot ru
Target Milestone: ---
Code:
#include <iostream>
#include <unordered_map>
using namespace std;
int main() {
std::unordered_map<int, int> x;
x.reserve(97);
std::cout << x.bucket_count() << std::endl;
for (int i = 0; i < 97; ++i) {
x[i] = 1;
}
std::cout << x.bucket_count() << std::endl;
}
it prints for me
97
199
It doesn't contradict my reading of the Standard but still counterintuitive.
If user reserves smth, he would expect no rehashes
Note, probably any prime will do.
Generally, for each as far as I understand rehashing happens when
new_size >= buckets_count (multiplied by load_factor which is 1)
I propose changing >= to >
