Iterating over a QHash VS std::unordered_map - c++

Question

#include <iostream>
#include <map>
#include <unordered_map>
#include <QHash>
#include <QMap>
#include <QString>
void _QMap()
{
QMap<int, QString> amap;
amap.insert(2, "cdasdc");
amap.insert(1, "cda");
amap.insert(3, "zzz");
std::cout << std::endl;
auto i = amap.begin();
while (i != amap.end())
std::cout << i.key() << " " << i++.value().toStdString() << std::endl;
}
void _map()
{
std::map<int, std::string> bmap;
std::pair<int, std::string> val(2, "cdasdc");
bmap.insert({1, "cda"});
bmap.insert({3, "zzz"});
bmap.insert(val);
std::cout << std::endl;
for (auto& i : bmap)
std::cout << i.first << " "<< i.second << std::endl;
}
void _QHash()
{
QHash<int, QString> ahash;
ahash.insert(2, "cdasdc");
ahash.insert(1, "cd");
ahash.insert(3, "zzz");
std::cout << std::endl;
auto i = ahash.begin();
while (i != ahash.end())
std::cout << i.key() << " " << i++.value().toStdString() << std::endl;
}
void _hash()
{
std::unordered_map<int, std::string> ahash;
ahash.insert({2, "cdasdc"});
ahash.insert({1, "cd"});
ahash.insert({3, "zzz"});
std::cout << std::endl;
for (auto& i : ahash)
std::cout << i.first << " "<< i.second << std::endl;
}
int main()
{
_QMap();
_map();
_QHash();
_hash();
}
I run above code multiple times and observed the output. The _QHash() print is different each time, which I was expecting since documentation says the items are arbitrarily ordered.
I was expecting QHash and std::unordered_map to behave the same way since documentation says the elements are not sorted.
However _hash() print is always the same. Why?

Answer 1

see https://doc.qt.io/qt-6/qhash.html#algorithmic-complexity-attacks
"In order to avoid this worst-case behavior, the calculation of the hash value done by qHash() can be salted by a random seed, that nullifies the attack's extent. This seed is automatically generated by QHash once per process, and then passed by QHash as the second argument of the two-arguments overload of the qHash() function.