我正在尝试使用 xercesc::XMLUri 作为键类型创建一个 std::unordered_map。
#include <unordered_map>
#include "xercesc/util/XMLUri.hpp"
int main()
{
std::unordered_map<xercesc::XMLUri,xercesc::XMLUri> uriMap;
}
结果如下:
clang++ -std=c++11 -O0 -emit-llvm -g3 -Wall -c -fmessage-length=0 -I/usr/include ../xx.cpp
In file included from ../xx.cpp:1:
In file included from /usr/bin/../lib/gcc/i686-linux-gnu/4.7/../../../../include/c++/4.7/unordered_map:43:
/usr/bin/../lib/gcc/i686-linux-gnu/4.7/../../../../include/c++/4.7/bits/functional_hash.h:59:7: error: static_assert failed "std::hash is not specialized for this type"
static_assert(sizeof(_Tp) < 0,
^ ~~~~~~~~~~~~~~~
/usr/bin/../lib/gcc/i686-linux-gnu/4.7/../../../../include/c++/4.7/bits/unordered_map.h:45:32: note: in instantiation of template class 'std::hash<xercesc_3_1::XMLUri>' requested here
integral_constant<bool, !__is_final(_Hash)>,
^
/usr/bin/../lib/gcc/i686-linux-gnu/4.7/../../../../include/c++/4.7/bits/unordered_map.h:263:14: note: in instantiation of default argument for '__unordered_map<xercesc_3_1::XMLUri, xercesc_3_1::XMLUri, std::hash<xercesc_3_1::XMLUri>, std::equal_to<xercesc_3_1::XMLUri>, std::allocator<std::pair<const xercesc_3_1::XMLUri, xercesc_3_1::XMLUri> > >' required here
: public __unordered_map<_Key, _Tp, _Hash, _Pred, _Alloc>
^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
../xx.cpp:6:54: note: in instantiation of template class 'std::unordered_map<xercesc_3_1::XMLUri, xercesc_3_1::XMLUri, std::hash<xercesc_3_1::XMLUri>, std::equal_to<xercesc_3_1::XMLUri>, std::allocator<std::pair<const xercesc_3_1::XMLUri, xercesc_3_1::XMLUri> > >' requested here
std::unordered_map<xercesc::XMLUri,xercesc::XMLUri> uriMap;
我知道 C++0x 中的无序容器只hash<>
为某些库类型提供专业化。如何创建所需的hash<xercesc::XMLUri>
专业化xercesc::XMLUri
?
编辑:我想出了这个。看起来合理吗?
#include "xercesc\util\XMLUri.hpp"
#include <string>
namespace std
{
size_t hash<xercesc::XMLUri>::operator()(const xercesc::XMLUri& uri) const
{
return hash<std::wstring>()(uri.getUriText());
}
}