Question

If I have a vector of strings how do I do a binary search for a certain string using a case-insensitive comparison? I can’t think of any easy way to do this.

Answer 1

Provide a comparison function to std::sort, sort your container in lower case (use boost string algos to help),

Then do a binary string on the sorted vector, again provide a case insensitive comparison operation to do this.

Using lambda expression will really help

If you use find it doesn’t have to be sorted first, however it is slow if you are going to doing frequent search and the set is quite large.

EDIT: here is the example

#include <boost/algorithm/string.hpp>
#include <algorithm>
::::

auto comp=[](const std::string& a, const std::string& b){   
   return boost::ilexicographical_compare
                       <std::string, std::string>(a,b);
});

std::sort(vs.begin(), vs.end(), comp);
std::binary_search(vs.begin(), vs.end(), value_to_search_for, comp);

The same comparison function would also work with std::find if you are not going to sort the list.

TESTED

http://en.cppreference.com/w/cpp/algorithm/find

http://en.cppreference.com/w/cpp/algorithm/binary_search

http://en.cppreference.com/w/cpp/algorithm/sort