Say you want to do a case-insensitive substring search in a locale-aware manner. For example, maybe you have a list of names, and you want the user to be able to search for them by typing any name fragment. A search for “ber” could find “Bert” as well as “Roberta”.<\/p>\n
I’ve seen people solve this problem by converting the string to lowercase, and then doing a code unit-based substring search. This technique doesn’t work for multiple reasons.<\/p>\n
One reason is that some languages (like English) do not consider diacritics significant in collation. The word naive<\/i> and na\u00efve<\/i> are considered equivalent for searching purposes. But a code unit substring search considers them different.<\/p>\n
For languages in which diacritics are significant, you have the problem of composed and decomposed characters. For example, the lowercase a with ring in the Swedish word n\u00e5gon<\/i> could be represented either as<\/p>\n The number of possibilities increases if you have characters with multiple diacritics. And then you also have ligatures, where the \ufb01<\/i> “fi” ligature is equivalent to two separate characters f<\/i> and i<\/i>.<\/p>\n So what’s the right thing to do?<\/p>\n In Windows, you can use the On other platforms, and even on Windows,\u00b2 you can use the ICU library’s string search service<\/a> and search with primary weight. (Primary weight honors diacritics which are significant to the locale.)<\/p>\n Bonus reading<\/b>: A popular but wrong way to convert a string to uppercase or lowercase<\/a>. What has case distinction but is neither uppercase nor lowercase<\/a>?<\/p>\n \u00b9 Throw in one of the \n
Find\u00adNLS\u00adString\u00adEx<\/code> function to do a locale-aware substring search. Use the LINGUISTIC_LINGUISTIC_IGNORE\u00adCASE<\/code> flags if you want a case-sensitive substring search.<\/p>\n