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sortingcomparesubscript-operator

what does the subscript operator mean in sort compare function?

struct pair{
    int first;
    int second;
}
vector<pair> v;
sort(v.begin(), v.end(), [](pair p1, pair p2){return p1.first < p2.first});

what does the [](pair p1, pair p2){return p1.first < p2.first} mean in sort? function pointer or anything else? I can't figure out the keywords to search.

Solution

  • this is a lambda expresion. See example below:

    void abssort(float* x, unsigned n) {
    std::sort(x, x + n,
        // Lambda expression begins
        [](float a, float b) {
            return (std::abs(a) < std::abs(b));
        } // end of lambda expression
    );
}
    1. reference: https://msdn.microsoft.com/en-us/library/dd293608.aspx

    the function that is being passed as a parameter does not have a "function name" - it is anonymous. This is a useful abstraction as all that is needed is the functionality that is being passed (the name does not matter).