How to write a multi value compare function for std::map

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  • Herby
    #1

    How to write a multi value compare function for std::map

    Hi,

    My key for the map is a class with two strings, group and name as
    follows:

    class ConfigKey{
    public:

    ConfigKey( String group, String key );

    String mGroup;
    String mName;
    };


    Now I want to do a lookup on both values matching.

    So I have defined my own compare functions as follows:

    struct cmp_config_key
    {
    bool operator()(Conf igKey const *lhs, ConfigKey const *rhs)
    {
    if( lhs->mGroup < rhs->mGroup ){
    if( lhs->mKey < rhs->mKey )
    return true;
    }

    return false;

    }
    };

    Above is not working correctly as it returns some other key when i
    call find. Im not too clear on this weak ordering business and it
    gets even more confusing with multiple values acting as the key.

    Naturally and intuitively i just want to write

    if( lhs->mGroup == rhs->mGroup ){
    if( lhs->mKey == rhs->mKey )
    return true;
    }

    Please could someone correct my function???


    Tags: None
    • Obnoxious User
      #2
      Re: How to write a multi value compare function for std::map

      On Mon, 10 Nov 2008 09:22:21 -0800, Herby wrote:
      Hi,
      >
      My key for the map is a class with two strings, group and name as
      follows:
      >
      class ConfigKey{
      public:
      >
      ConfigKey( String group, String key );
      >
      String mGroup;
      String mName;
      };
      >
      >
      Now I want to do a lookup on both values matching.
      >
      So I have defined my own compare functions as follows:
      >
      struct cmp_config_key
      {
      bool operator()(Conf igKey const *lhs, ConfigKey const *rhs) {
      if( lhs->mGroup < rhs->mGroup ){
      if( lhs->mKey < rhs->mKey )
      return true;
      }
      >
      return false;
      >
      }
      };
      >
      Above is not working correctly as it returns some other key when i call
      find. Im not too clear on this weak ordering business and it gets even
      more confusing with multiple values acting as the key.
      >
      Naturally and intuitively i just want to write
      >
      if( lhs->mGroup == rhs->mGroup ){
      if( lhs->mKey == rhs->mKey )
      return true;
      }
      >
      Please could someone correct my function???
      struct cmp_config_key
      {
      bool operator()(Conf igKey const *lhs, ConfigKey const *rhs) const
      {
      if(lhs->mGroup < rhs->mGroup) {
      return true;
      }
      if(lhs->mGroup == rhs->mGroup) {
      if(lhs->mKey < rhs->mKey) {
      return true;
      }
      }
      return false;
      }
      };

      --
      OU
      Remember 18th of June 2008, Democracy died that afternoon.
      http://frapedia.se/wiki/Information_in_English

        Comment

        • Herby
          #3
          Re: How to write a multi value compare function for std::map

          On Nov 10, 5:58 pm, Obnoxious User <O...@127.0.0.1 wrote:
          On Mon, 10 Nov 2008 09:22:21 -0800, Herby wrote:
          Hi,
          >
          My key for the map is a class with two strings, group and name as
          follows:
          >
          class ConfigKey{
          public:
          >
          ConfigKey( String group, String key );
          >
          String mGroup;
          String mName;
          };
          >
          Now I want to do a lookup on both values matching.
          >
          So I have defined my own compare functions as follows:
          >
          struct cmp_config_key
          {
          bool operator()(Conf igKey const *lhs, ConfigKey const *rhs) {
          if( lhs->mGroup < rhs->mGroup ){
          if( lhs->mKey < rhs->mKey )
          return true;
          }
          >
          return false;
          >
          }
          };
          >
          Above is not working correctly as it returns some other key when i call
          find. Im not too clear on this weak ordering business and it gets even
          more confusing with multiple values acting as the key.
          >
          Naturally and intuitively i just want to write
          >
          if( lhs->mGroup == rhs->mGroup ){
          if( lhs->mKey == rhs->mKey )
          return true;
          }
          >
          Please could someone correct my function???
          >
          struct cmp_config_key
          {
          bool operator()(Conf igKey const *lhs, ConfigKey const *rhs) const
          {
          if(lhs->mGroup < rhs->mGroup) {
          return true;
          }
          if(lhs->mGroup == rhs->mGroup) {
          if(lhs->mKey < rhs->mKey) {
          return true;
          }
          }
          return false;
          }
          >
          };
          >
          --
          OU
          Remember 18th of June 2008, Democracy died that afternoon.http://frapedia.se/wiki/Information_in_English
          Thanks mate. Excellent works!!!!!

            Comment

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