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STL - Map question

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Started by JoeyBlow2 March 05, 2006 04:48 PM

2 comments, last by JoeyBlow2 18 years, 1 month ago

JoeyBlow2

100

Author

March 05, 2006 04:48 PM

Can you have a map such as this?



std::map<sockaddr_in, long>

sockaddr_in is defined in the winsock2.h. I want to be able to take an incoming ipaddress/port and convert it into an index. However, I get errors doing that.



1>f:\vs8\vc\include\functional(143) : error C2784: 'bool std::operator <(const std::_Tree<_Traits> &,const std::_Tree<_Traits> &)' :
could not deduce template argument for 'const std::_Tree<_Traits> &' from 'const sockaddr_in'

Any ideas on how to fix this?

rip-off

11,000

March 05, 2006 04:54 PM

Give it a compare function/functor.

E.g.

struct CompareIP{   bool operator()( const sockaddr_in &one, const sockaddr_in &two ) const   {      if( one.host < two.host )      {         return true;      }      return one.port < two.port;   }};std::map<sockaddr_in, long, CompareIP>

[Edited by - Fruny on March 6, 2006 12:54:45 AM]

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leiavoia

960

March 05, 2006 08:09 PM

Usually you overload the '<' operator for your class. The reason is because a std::map is sorted into a tree internally, and if there is no way of comparing one object to another the map will not know how to sort them.

If you want a cheap way of doing it, it is possible to map a class pointer to something though, since it is very easy to compare pointer addresses (they are just numbers afterall). So you could have this:

std::map<Foo*, Bar>

JoeyBlow2

100

Author

March 06, 2006 12:25 PM

Thanks for the help. :)

STL - Map question

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