I have the following program. I built it with gcc-4.9.2 under linux. My questions are:
1) Why does the hashtable seem to be sorted the first time around, but loses the sort after the items are deleted from value?
2) How do I walk the hashtable by key myself and say std::cout each item that hashes to a bucket, e.g., the code in the #if 0 #endif section?
#include <vector>
#include <iostream>
#include <vector>
#include <functional>
#include <boost/intrusive/unordered_set.hpp>
namespace bic = boost::intrusive;
std::hash<std::string> hash_fn;
struct MyClass : bic::unordered_set_base_hook<bic::link_mode<bic::auto_unlink>>
{
std::string name;
int anInt1;
mutable bool bIsMarkedToDelete;
MyClass(std::string name, int i) : name(name), anInt1(i), bIsMarkedToDelete(false) {}
bool operator==(MyClass const& o) const
{
//return anInt1 == o.anInt1 && name == o.name;
return name == o.name;
}
struct hasher
{
size_t operator()(MyClass const& o) const
{
return o.anInt1;
//return hash_fn(o.name);
}
};
};
std::ostream& operator << (std::ostream& out, const MyClass& ac)
{
std::cout << ac.name << " " << ac.anInt1;
return out;
}
typedef bic::unordered_set<MyClass, bic::hash<MyClass::hasher>, bic::constant_time_size<false> > HashTable;
int main()
{
std::vector<MyClass> values
{
MyClass { "John", 0 },
MyClass { "Mike", 0 },
MyClass { "Dagobart", 25 },
MyClass { "John", 5 },
MyClass { "Mike", 25 },
MyClass { "Dagobart", 26 },
MyClass { "John", 10 },
MyClass { "Mike", 25 },
MyClass { "Dagobart", 27 },
MyClass { "John", 15 },
MyClass { "Mike", 27 }
};
HashTable::bucket_type buckets[100];
HashTable hashtable(values.begin(), values.end(), HashTable::bucket_traits(buckets, 100));
std::cout << "\nContents of std::vector<MyClass> values\n";
for(auto& e: values)
std::cout << e << " ";
std::cout << "\nContents of HashTable hashtable\n";
for(auto& b : hashtable)
std::cout << b << '\n';
#if 0 // This code won't compile since there is no operator [] for hashtable
for(int bucket = 0; bucket < 27; bucket++)
{
auto hit(hashtable[bucket].rbegin());
auto hite(hashtable[bucket].rend());
while (hit != hite)
{
MyClass mc = *hit;
std::cout << mc << " ";
hit++;
}
std::cout << '\n';
}
#endif // 0
std::cout << '\n';
std::cout << "values size first " << values.size() << '\n';
std::cout << "hash size fist " << hashtable.size() << '\n';
for(auto& e: values)
e.bIsMarkedToDelete |= ("Mike" == e.name);
std::cout << "removing all bIsMarkedToDelete";
for(auto& e: values)
if(e.bIsMarkedToDelete)
std::cout << e << " ";
std::cout << '\n';
values.erase(
std::remove_if(std::begin(values), std::end(values), std::mem_fn(&MyClass::bIsMarkedToDelete)),
std::end(values));
std::cout << "values size now " << values.size() << '\n';
std::cout << "hash size now " << hashtable.size() << '\n';
std::cout << "Contents of value after removing elements " << '\n';
for(auto& e: values)
std::cout << e << " ";
std::cout << "\nContents of HashTable hashtable after delete Mike\n";
for(auto& b : hashtable)
std::cout << b << '\n';
std::cout << '\n';
values.clear();
std::cout << values.size() << '\n';
std::cout << hashtable.size() << '\n';
std::cout << "Done\n";
int j;
std::cin >> j;
}
