问题
I want to use a std::map
whose key and value elements are structures.
I get the following error:
error C2784: 'bool std::operator <(const std::basic_string<_Elem,_Traits,_Alloc> &,const _Elem *)' : could not deduce template argument for 'const std::basic_string<_Elem,_Traits,_Alloc> &' from 'const GUID
I understand that I should overload operator <
for that case, but the thing is I don't have access to the code of the structure I want to use (GUID
structure in VC++).
Here's the code snippet:
//.h
#include <map>
using namespace std;
map<GUID,GUID> mapGUID;
//.cpp
GUID tempObj1, tempObj2;
mapGUID.insert( pair<GUID,GUID>(tempObj1, tempObj2) );
How to solve this problem?
回答1:
You can define the comparison operator as a freestanding function:
bool operator<(const GUID & Left, const GUID & Right)
{
// comparison logic goes here
}
Or, since in general a < operator does not make much sense for GUIDs, you could instead provide a custom comparison functor as the third argument of the std::map
template:
struct GUIDComparer
{
bool operator()(const GUID & Left, const GUID & Right) const
{
// comparison logic goes here
}
};
// ...
std::map<GUID, GUID, GUIDComparer> mapGUID;
回答2:
Any type you use as a key has to provide a strict weak ordering. You can supply a comparator type as a third template argument, or you can overload operator<
for your type.
回答3:
There is no operator < for GUIDS so you either have to provide the comparison operator or use a different key.
回答4:
May be using class inherited from GUID in which you implement operator < would be a workaround for you?
来源:https://stackoverflow.com/questions/5353287/how-to-use-struct-as-key-in-stdmap