Sorting array of classes

[mighty asker]

Hello. I used this ( http://www.cplusplus.com/forum/general/97555/#msg523529 ) example to sort an array of classes. But what if I want to modify "Option 1" (made by Stewbond) so that if lhs.num1==rhs.num1 the program would remain sorting by another member (num2 in this example)?

[MiiNiPaa]

#include <algorithm>
#include <tuple>
struct a
{
    int num1;
    int num2;
};

bool acompare(a lhs, a rhs) 
{ 
    return std::tie(lhs.num1, lhs.num2) < std::tie(rhs.num1, rhs.num2);
}

int main()
{
   a array[1000];
   std::sort(array, array+1000, acompare);
}

[mighty asker]

Thank you. This seems to work. Could you explain me how?

[MiiNiPaa]

std::tie returns a tuple of references. And tuples already have well-defined comparison behavior: it compares first elements, if they equal, it compares seconds and so on.