upper_bound/lower_bound function in C++

Question

I'm trying to find the upper and lower bounds of my vector (vector possible) using these functions. The struct data holds 3 strings and I'm using string date for comparison.

bool myCompare(Data &a, Data &b) {
      return (a.date == b.date);
}

#include <algorithm>

     std::vector<Data>::iterator iterl, iteru;
     sort(possible.begin(), possible.end(), compare);
     iterl = std::lower_bound(possible.begin(), possible.end(), struct1, myCompare);
     iteru = std::upper_bound(possible.begin(), possible.end(), struct2, myCompare);

but by doing that, the compiler is displayng the following message:

Main.cpp:95:18: note: in instantiation of function template specialization 'std::__1::upper_bound<std::__1::__wrap_iter<data *>,
data, bool (*)(data &, data &)>' requested here
iteru = std::upper_bound(possible.begin(), possible.end(), struct2, myCompare);

whats the proper way to use these functions?

You should use strict weak ordering predicate (e.g. less) to compare: a.date < b.date — AlexT, Apr 01 '14 at 08:26
Better to use const references: `bool myCompare(const Data &a, const Data &b)` — AlexT, Apr 01 '14 at 08:27

score 1 · Answer 1 · answered Apr 01 '14 at 08:28

1

The signature for the comparison object is bool cmp(const Type1 &a, const Type2 &b);, you need to add const to the arguments of myCompare.

answered Apr 01 '14 at 08:28

user657267

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AlexT · Answer 2 · 2014-04-01T08:37:46.257

Perhaps the best that you can do is to define operator< for Date and don't use predicates with algorithm explicitely

bool operator<(const Data& lhs, const Data& rhs)
{
    return lhs.date < rhs.date;
}

std::vector<Data>::iterator iterl, iteru;
sort(possible.begin(), possible.end());
iterl = std::lower_bound(possible.begin(), possible.end(), data1);
iteru = std::upper_bound(possible.begin(), possible.end(), data2);

upper_bound/lower_bound function in C++

2 Answers2