Case insensitive std::string.find()

Question

I am using std::string\'s find() method to test if a string is a substring of another. Now I need case insensitive version of the same thing. For s

Answer 1

I love the answers from Kiril V. Lyadvinsky and CC. but my problem was a little more specific than just case-insensitivity; I needed a lazy Unicode-supported command-line argument parser that could eliminate false-positives/negatives when dealing with alphanumeric string searches that could have special characters in the base string used to format alphanum keywords I was searching against, e.g., Wolfjäger shouldn't match jäger but <jäger> should.

It's basically just Kiril/CC's answer with extra handling for alphanumeric exact-length matches.

/* Undefined behavior when a non-alpha-num substring parameter is used. */
bool find_alphanum_string_CI(const std::wstring& baseString, const std::wstring& subString)
{
    /* Fail fast if the base string was smaller than what we're looking for */
    if (subString.length() > baseString.length()) 
        return false;

    auto it = std::search(
        baseString.begin(), baseString.end(), subString.begin(), subString.end(),
        [](char ch1, char ch2)
        {
            return std::toupper(ch1) == std::toupper(ch2);
        }
    );

    if(it == baseString.end())
        return false;

    size_t match_start_offset = it - baseString.begin();

    std::wstring match_start = baseString.substr(match_start_offset, std::wstring::npos);

    /* Typical special characters and whitespace to split the substring up. */
    size_t match_end_pos = match_start.find_first_of(L" ,<.>;:/?\'\"[{]}=+-_)(*&^%$#@!~`");

    /* Pass fast if the remainder of the base string where
       the match started is the same length as the substring. */
    if (match_end_pos == std::wstring::npos && match_start.length() == subString.length()) 
        return true;

    std::wstring extracted_match = match_start.substr(0, match_end_pos);

    return (extracted_match.length() == subString.length());
}

Answer 2

If you want “real” comparison according to Unicode and locale rules, use ICU’s Collator class.

Answer 3

wxWidgets has a very rich string API wxString

it can be done with (using the case conversion way)

int Contains(const wxString& SpecProgramName, const wxString& str)
{
  wxString SpecProgramName_ = SpecProgramName.Upper();
  wxString str_ = str.Upper();
  int found = SpecProgramName.Find(str_);
  if (wxNOT_FOUND == found)
  {
    return 0;
  }
  return 1;
}

Answer 4

Why not just convert both strings to lowercase before you call find()?

tolower

Notice:

• Inefficient for long strings.
• Beware of internationalization issues.