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 string comparison I can always turn to stricmp   but there doesn t seem to be a stristr     I have found various answers and most suggest using Boost which is not an option in my case   Additionally  I need to support std  wstring wchar t  Any ideas

User · Answer

If you want    real    comparison according to Unicode and locale rules  use ICU   s Collator class

User · Answer

why not use Boost StringAlgo    include  lt boost algorithm string find hpp gt   bool Foo          case insensitive find     std  string str  Hello        boost  iterator range lt std  string  const iterator gt  rng      rng   boost  ifind first str  std  string  EL         return rng

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wxWidgets has a very rich string API  wxString  it can be done with  using the case conversion way   int Contains const wxString amp  SpecProgramName  const wxString amp  str      wxString SpecProgramName    SpecProgramName Upper      wxString str    str Upper      int found   SpecProgramName Find str      if  wxNOT FOUND    found          return 0        return 1

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Why not just convert both strings to lowercase before you call find     tolower  Notice    Inefficient for long strings  Beware of internationalization issues

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You could use std  search with a custom predicate    include  lt locale gt   include  lt iostream gt   include  lt algorithm gt  using namespace std      templated version of my equal so it could work with both char and wchar t template lt typename charT gt  struct my equal       my equal  const std  locale amp  loc     loc  loc         bool operator   charT ch1  charT ch2            return std  toupper ch1  loc      std  toupper ch2  loc          private      const std  locale amp  loc          find substring  case insensitive  template lt typename T gt  int ci find substr  const T amp  str1  const T amp  str2  const std  locale amp  loc   std  locale           typename T  const iterator it   std  search  str1 begin    str1 end             str2 begin    str2 end    my equal lt typename T  value type gt  loc         if   it    str1 end     return it - str1 begin        else return -1     not found    int main int arc  char  argv              string test     std  string str1    FIRST HELLO       std  string str2    hello       int f1   ci find substr  str1  str2            wstring test     std  wstring wstr1   L                    std  wstring wstr2   L              int f2   ci find substr  wstr1  wstr2         return 0

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Also make sense to provide Boost version  This will modify original strings    include  lt boost algorithm string hpp gt   string str1    hello world      string str2    HELLO   boost  algorithm  to lower str1  boost  algorithm  to lower str2   if  str1 find str2     std  string  npos           str1 contains str2     or using perfect boost xpression library    include  lt boost xpressive xpressive hpp gt  using namespace boost  xpressive       std  string long string   very LonG string     std  string word  long    smatch what  sregex re   sregex  compile word  boost  xpressive  icase   if  regex match  long string  what  re           cout  lt  lt  word  lt  lt    found    lt  lt  endl      In this example you should pay attention that your search word don t have any regex special characters

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The new C  11 style    include  lt algorithm gt   include  lt string gt   include  lt cctype gt       Try to find in the Haystack the Needle - ignore case bool findStringIC const std  string  amp  strHaystack  const std  string  amp  strNeedle      auto it   std  search      strHaystack begin    strHaystack end        strNeedle begin      strNeedle end           char ch1  char ch2    return std  toupper ch1     std  toupper ch2            return  it    strHaystack end          Explanation of the std  search can be found on cplusplus com

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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   Wolfj  ger shouldn t match j  ger but  lt j  ger gt  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 amp  baseString  const std  wstring amp  subString           Fail fast if the base string was smaller than what we re looking for        if  subString length    gt  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    lt   gt               -     amp                     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  amp  amp  match start length      subString length             return true       std  wstring extracted match   match start substr 0  match end pos        return  extracted match length      subString length

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include  lt iostream gt  using namespace std   template  lt typename charT gt  struct ichar       operator charT   const   return toupper x         charT x     template  lt typename charT gt  static basic string lt ichar lt charT gt   gt   istring basic string lt charT gt   amp s    return  basic string lt ichar lt charT gt   gt     amp s    template  lt typename charT gt  static ichar lt charT gt   istring const charT  s    return  ichar lt charT gt    s     int main         string s    The STRING       wstring ws   L The WSTRING       cout  lt  lt  istring s - gt find istring  str     lt  lt       lt  lt  istring ws - gt find istring L wstr      lt  lt  endl      A little bit dirty  but short  amp  fast

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Since you re doing substring searches  std  string  and not element  character  searches  there s unfortunately no existing solution I m aware of that s immediately accessible in the standard library to do this   Nevertheless  it s easy enough to do  simply convert both strings to upper case  or both to lower case - I chose upper in this example    std  string upper string const std  string amp  str        string upper      transform str begin    str end    std  back inserter upper   toupper       return upper     std  string  size type find str ci const std  string amp  str  const std  string amp  substr        return upper str  find upper substr         This is not a fast solution  bordering into pessimization territory  but it s the only one I know of off-hand  It s also not that hard to implement your own case-insensitive substring finder if you are worried about efficiency      Additionally  I need to support   std  wstring wchar t  Any ideas    tolower toupper in locale will work on wide-strings as well  so the solution above should be just as applicable  simple change std  string to std  wstring     Edit  An alternative  as pointed out  is to adapt your own case-insensitive string type from basic string by specifying your own character traits  This works if you can accept all string searches  comparisons  etc  to be case-insensitive for a given string type

[c++] Case insensitive std::string.find()

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