creating a << operator

This is a discussion on creating a << operator within the C++ Programming forums, part of the General Programming Boards category; I have a map <string, vector of ints> and would like to display what I hope I have loaded into ...

  1. #1
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    creating a << operator

    I have a map <string, vector of ints> and would like to display what I hope I have loaded into the map...however, it appears that I have to define a << operator that takes a type HEADINGMAP (my map type).

    Could anyone pls assist.
    Thanks
    s

  2. #2
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    This is the best I can do with what little detail you've provided.
    Code:
    ostream& operator<<(ostream& out, const HEADINGMAP& hmap)
    {
      // Code to write the contents of hmap to out
      return out;
    }
    When writing a specialization, be careful about its location; or to make it compile will be such a trial as to kindle its self-immolation.

  3. #3
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    creating a << operator

    Thanks Kip,

    I have included your code - but am now getting compile errors...

    error C2143: syntax error : missing ',' before '&'

    does hmap have to be declared elsewhere - in a .h ?? It says it is undeclared...

    I have tried to use:
    out << *hmap->first << ": ";

    to display the string portion of the map, but am getting a compile error - error C2227: left of '->first' must point to class/struct/union

    I need to be able to access the key and values within the map - in order to write them to a report.
    Thanks for your help
    sue

  4. #4
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    Quote Originally Posted by Sue Paterniti
    Thanks Kip,

    I have included your code - but am now getting compile errors...

    error C2143: syntax error : missing ',' before '&'

    does hmap have to be declared elsewhere - in a .h ?? It says it is undeclared...

    I have tried to use:
    out << *hmap->first << ": ";

    to display the string portion of the map, but am getting a compile error - error C2227: left of '->first' must point to class/struct/union

    I need to be able to access the key and values within the map - in order to write them to a report.
    Thanks for your help
    sue
    This has all the signs of HEADINGMAP not being a type. What does the declaration of HEADINGMAP look like? I was under the impression that you were doing something like this.
    Code:
    typedef map< string, vector<int> > HEADINGMAP;
    
    [...]
    
    ostream& operator<<(ostream& out, const HEADINGMAP& hmap)
    {
      HEADINGMAP::const_iterator i = hmap.begin();
    
      for (; i != hmap.end(); ++i) {
        out << i->first << ": ";
      }
    
      return out;
    }
    When writing a specialization, be careful about its location; or to make it compile will be such a trial as to kindle its self-immolation.

  5. #5
    Registered User eth0's Avatar
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    Sue,
    You need to read up on operator overloading. Then you'll be able to make sense of Kips code and implement it into your code.

    Its not a large topic for what you need, and should help you.

    hth
    Open source isn't a matter of life or death......
    .......its much more important than that!!


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  6. #6
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    Hi Kip,
    I have typedef'd an int vector as typedef vector<int> INTVEC;
    Then typdef'd the map as typedef map <string, INTVEC > HEADINGMAP;
    and an iterator as typedef HEADINGMAP::iterator HEADMAPIT;

    am still getting the compile error that there is a missing ',' before a '&' - but will do some more reading as recommended...
    thanks
    s

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