post  relationship between string bool operator and map container class

kenr (7)   Link to this post
Sorry gents but I'm still not clear how the bool operator function relates to the <map> container class. I understand the common element between them is the class X but fail to see how the <map> operates on the bool operator function. The compiler freeks if I remove comment out the bool operator function??


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class X
{
    ...
};

class Y
{
    ...
};

bool operator < (const X& first, const X& second)
{
    return first.memberofX < second.memberofX;
}

int main()
{
    map<X, Y> mymap;

    ...
    
    return 0;
}

kempofighter (668)   Link to this post
std::map is an associative array that uses an internal binary tree. It must keep all pairs sorted by the key value. Therefore whatever you use as the key_type, in this case the X type, the std::map must be able to compare instances of type X against one another. You'd have the same problem with the std::set if you wanted to fill it with X objects. Read std::map's documentation more closely and study the examples provided on this site.

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