problem defening a map of structs

This is a discussion on problem defening a map of structs within the C++ Programming forums, part of the General Programming Boards category; hello, I try to define a map of structs. What I have is this : Code: #include <iostream> #include <map> ...

  1. #1
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    problem defening a map of structs

    hello,

    I try to define a map of structs.

    What I have is this :
    Code:
    #include <iostream>
    #include <map>
    #include <string>
    
    using namespace std;
    
    int main() {
    
    struct teamstats {
    string team_name;
    int played_games, point_made, points_against;
    }
    
    map<string, struct teamstats> allteams;
    
    }
    I see now this message :

    C:\Users\wobben\Desktop\toernooi\test\main.cpp|14| error: template argument for 'template<class _T1, class _T2> struct std:air' uses local type 'main()::teamstats'|

    Can someone explain what went wrong here ?

    Roelof

  2. #2
    C++ Witch laserlight's Avatar
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    You should define the struct outside of the main function, with a trailing semi-colon and proper indentation, e.g.,
    Code:
    #include <iostream>
    #include <map>
    #include <string>
    
    using namespace std;
    
    struct teamstats {
        string team_name;
        int played_games, point_made, points_against;
    };
    
    int main() {
        map<string, teamstats> allteams;
    }
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  3. #3
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    Oke,

    Solved,
    Now can i test if I can read the data from a file and put it into the struct.

    Roelof

  4. #4
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    Ike,

    Last question I hope,

    Can I sort the map first on game_points and if there the same on played_games.

    Roelof

  5. #5
    C++まいる!Cをこわせ! Elysia's Avatar
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    A map is not meant to be sorted. It simply allows you to map one type to another.
    Quote Originally Posted by Adak View Post
    io.h certainly IS included in some modern compilers. It is no longer part of the standard for C, but it is nevertheless, included in the very latest Pelles C versions.
    Quote Originally Posted by Salem View Post
    You mean it's included as a crutch to help ancient programmers limp along without them having to relearn too much.

    Outside of your DOS world, your header file is meaningless.

  6. #6
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    Oke,

    Then I have a problem.
    The outcome of the reading of the file and processing it , must be sorted so I can make a good ranking.

    back to the drawing board.

    Roelof

  7. #7
    C++まいる!Cをこわせ! Elysia's Avatar
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    You can use another container. For example, iterate your map, take every element, put it into a vector, sort it, then print your results.
    Quote Originally Posted by Adak View Post
    io.h certainly IS included in some modern compilers. It is no longer part of the standard for C, but it is nevertheless, included in the very latest Pelles C versions.
    Quote Originally Posted by Salem View Post
    You mean it's included as a crutch to help ancient programmers limp along without them having to relearn too much.

    Outside of your DOS world, your header file is meaningless.

  8. #8
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    oke,

    So read the map teamstats.
    Copy everything to a container of vectors and then sort it.

    Do I understand you right.
    And can a container of vectors be sorted on multiple arguments.
    Can I then not using a container of vectors in the first place ?

    Roelof

  9. #9
    C++まいる!Cをこわせ! Elysia's Avatar
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    A vector (or any other container that is sortable) can be sorted by multiple values. You decide exactly how to sort it by implementing your operator <.
    Could you use it from the beginning? I don't know. I haven't followed what exactly you do.
    Quote Originally Posted by Adak View Post
    io.h certainly IS included in some modern compilers. It is no longer part of the standard for C, but it is nevertheless, included in the very latest Pelles C versions.
    Quote Originally Posted by Salem View Post
    You mean it's included as a crutch to help ancient programmers limp along without them having to relearn too much.

    Outside of your DOS world, your header file is meaningless.

  10. #10
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    What I try to do is this.

    my struct looks like this :
    string team_name
    int played_games, game_points, made_points, against_points.

    Read a line from a text file.
    and put the content of that file to these variables : home_team, away_team, home_score and away_score.

    Then test if home_team is not already in the container.
    If so do this :
    increase played games for that team by 1
    look if that team has won , if so increase game_points by 3
    increase
    Increase made_points and against_points by the score of that game.

    The same story of the away_team.

    Read the following line and start over again with the home_team.

    If the whole file is read to the end.
    Sort everything and print it out.

    Roelof

    Edit :

    I see what's the problem is with vector containers.
    I don't know how many teams there are so I can't define the container well.
    Or make use of resize when finding a new team.
    Last edited by roelof; 06-05-2010 at 04:09 AM.

  11. #11
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    Second problem
    I have this code:
    Code:
    #include <iostream>
    #include <map>
    #include <string>
    #include <fstream>
    
    using namespace std;
    
    struct teamstats {
        string team_name;
        int played_games, point_made, points_against;
    };
    
    int main() {
        map<string, teamstats> allteams;
        string str,myBuf;
    
        ifstream a_file ("test.txt");
        a_file >> str ;
        cout << str ;
     return 0 ;
    }
    Why gives cout no output.
    The file test.txt exist with one rule.

    Roelof

  12. #12
    spurious conceit MK27's Avatar
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    Try adding a few lines to make sure, and read the whole file:
    Code:
    int main() {
        map<string, teamstats> allteams;
        string str,myBuf;
    
        ifstream a_file ("test.txt");
        if (!a_file.good()) cerr << "File not found!\n";
        while (a_file >> str) cout << str ;
    
        return 0 ;
    }
    Nb, this method of reading the file chomps newlines.
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    GNU C Function and Macro Index -- glibc reference manual
    The C Book -- nice online learner guide
    Current ISO draft standard
    CCAN -- new CPAN like open source library repository
    3 (different) GNU debugger tutorials: #1 -- #2 -- #3
    cpwiki -- our wiki on sourceforge

  13. #13
    Super Moderator VirtualAce's Avatar
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    You can use another container. For example, iterate your map, take every element, put it into a vector, sort it, then print your results.
    I actuall do this quite often. Many tests have revealed that iterating a map is far slower than iterating a vector although the code looks identical. Normally I build a vector from the items being used in the map and when the map changes I clear the vector and re-build it from the map. The easiest thing to do is to actually store map iterators in the vector so that when you iterate the vector you gain instant access to the map and it does not require an O(n log n) lookup per item in the vector. This works fine as long as you protect the map and make sure that if something is removed from the map the vector is updated to reflect this. If not you could have invalid iterators in the vector.

  14. #14
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    store your strings (keys) in a vector, implement a sorting function based on the contents of the map value.

    then you can print them in your order, I dont see why its recommended to use another container?

  15. #15
    Super Moderator VirtualAce's Avatar
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    ...dont see why its recommended to use another container?
    Perhaps to support fast removal and insertion. Vectors are not good for insertion or removal since iterators beyond the point of removal are invalidated.

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