Case insensitive string::find

Question

Is there exist a case-insensitive find() method for std::string?

Answer 1

You could upper-case both strings and use the regular find. (Note: this approach may not be correct if you have Unicode string.)

In Boost there's also ifind_first for case-insensitive search. (note that it returns a range instead of a size_t).

#include <string>
#include <boost/algorithm/string/find.hpp>
#include <cstdio>
#include <cctype>

std::string upperCase(std::string input) {
  for (std::string::iterator it = input.begin(); it != input.end(); ++ it)
    *it = toupper(*it);
  return input;
}

int main () {
  std::string foo = "1 FoO 2 foo";
  std::string target = "foo";

  printf("string.find: %zu\n", foo.find(target));

  printf("string.find w/ upperCase: %zu\n", upperCase(foo).find(upperCase(target)));

  printf("ifind_first: %zu\n", boost::algorithm::ifind_first(foo, target).begin() - foo.begin());

  return 0;
}

Answer 2

this is what I would have suggested, (the same as @programmersbook)

#include <iostream>
#include <algorithm>
#include <string>

bool lower_test (char l, char r) {
  return (std::tolower(l) == std::tolower(r));
}

int main()
{
  std::string text("foo BaR");
  std::string search("bar");

  std::string::iterator fpos = std::search(text.begin(), text.end(), search.begin(), search.end(), lower_test);
  if (fpos != text.end())
    std::cout << "found at: " << std::distance(text.begin(), fpos) << std::endl;
  return 0;
}

Answer 3

Before doing anything fancy, have a look at

http://www.gotw.ca/gotw/029.htm

and see if using a custom character traits class is not what you want.