[Seqan-dev] CharString as a key in an unordered_map

[Oliver Stolpe <oliver.stolpe@fu-berlin.de>]

Hello list,

I try to use a SeqAn CharString as a key in an unordered_map (C++11). It 
fails when he tries to link. The linker message is posted below. I think 
the CharString type is not hashable, therefore I probably need to 
provide my own hash function (see below). Am I heading in the right 
direction? Before I start doing this I wanted to know why a string is 
hashable by the default function but not a CharString? Is there a trick 
to easily get around this?

Thanks,
Oliver


This is my map structure:

unordered_map<CharString, unsigned int>

I assume I have to do something like this to provide a hash function 
(found at stackoverflow):

template<>
struct hash<typename CharString> {
  size_t operator() (CharString const &key) {
     // calculate hash value
  }
};

Linker message:

Linking CXX executable fastq_reader
CMakeFiles/fastq_reader.dir/fastq_reader.cpp.o: In function 
`std::_Hashtable<seqan::String<char, seqan::Alloc<void> >, 
std::pair<seqan::String<char, seqan::Alloc<void> > const, unsigned int>, 
std::allocator<std::pair<seqan::String<char, seqan::Alloc<void> > const, 
unsigned int> >, std::_Select1st<std::pair<seqan::String<char, 
seqan::Alloc<void> > const, unsigned int> >, 
std::equal_to<seqan::String<char, seqan::Alloc<void> > >, 
std::hash<seqan::String<char, seqan::Alloc<void> > >, 
std::__detail::_Mod_range_hashing, std::__detail::_Default_ranged_hash, 
std::__detail::_Prime_rehash_policy, false, false, 
true>::find(seqan::String<char, seqan::Alloc<void> > const&)':
fastq_reader.cpp:(.text._ZNSt10_HashtableIN5seqan6StringIcNS0_5AllocIvEEEESt4pairIKS4_jESaIS7_ESt10_Select1stIS7_ESt8equal_toIS4_ESt4hashIS4_ENSt8__detail18_Mod_range_hashingENSF_20_Default_ranged_hashENSF_20_Prime_rehash_policyELb0ELb0ELb1EE4findERS6_[std::_Hashtable<seqan::String<char, 
seqan::Alloc<void> >, std::pair<seqan::String<char, seqan::Alloc<void> > 
const, unsigned int>, std::allocator<std::pair<seqan::String<char, 
seqan::Alloc<void> > const, unsigned int> >, 
std::_Select1st<std::pair<seqan::String<char, seqan::Alloc<void> > 
const, unsigned int> >, std::equal_to<seqan::String<char, 
seqan::Alloc<void> > >, std::hash<seqan::String<char, seqan::Alloc<void> 
> >, std::__detail::_Mod_range_hashing, 
std::__detail::_Default_ranged_hash, 
std::__detail::_Prime_rehash_policy, false, false, 
true>::find(seqan::String<char, seqan::Alloc<void> > const&)]+0x8a): 
undefined reference to `std::hash<seqan::String<char, seqan::Alloc<void> 
> >::operator()(seqan::String<char, seqan::Alloc<void> >) const'
collect2: ld gab 1 als Ende-Status zurück