How to get the number of characters in a std string

Question

How should I get the number of characters in a string in C

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std  string str  a string    std  cout  lt  lt  str size    lt  lt  std  endl

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for an actual string object   yourstring length      or  yourstring size

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if you re using std  string  there are two common methods for that   std  string Str  Some String    size t Size   0  Size   Str size    Size   Str length      if you re using the C style string  using char   or const char    then you can use   const char  pStr    Some String   size t Size   strlen pStr

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In C   std  string the length   and size   method gives you the number of bytes  and not necessarily the number of characters     Same with the c-Style sizeof   function   For most of the printable 7bit-ASCII Characters this is the same value  but for characters that are not 7bit-ASCII it s definitely not  See the following example to give you real results  64bit linux     There is no simple c c   function that can really count the number of characters  By the way  all of this stuff is implementation dependent and may be different on other environments  compiler  win 16 32  linux  embedded        See following example    include  lt string gt   include  lt iostream gt   include  lt stdio h gt   include  lt string h gt  using namespace std   int main        c-Style char Array    const char   Test1    1234   const char   Test2                const char   Test3    a          c   string object    string sTest1    1234   string sTest2                string sTest3    a       printf   r nC Style Resluts  r n    printf  Test1   s  strlen     d r n  Test1   int  strlen Test1    printf  Test2   s  strlen     d r n  Test2   int  strlen Test2    printf  Test3   s  strlen     d r n  Test3   int  strlen Test3     printf   r nC   Style Resluts  r n    cout  lt  lt   Test1     lt  lt  sTest1  lt  lt     Test1 size        lt  lt sTest1 size    lt  lt    sTest1 length       lt  lt  sTest1 length    lt  lt  endl  cout  lt  lt   Test1     lt  lt  sTest2  lt  lt     Test2 size        lt  lt sTest2 size    lt  lt    sTest1 length       lt  lt  sTest2 length    lt  lt  endl  cout  lt  lt   Test1     lt  lt  sTest3  lt  lt     Test3 size       lt  lt sTest3 size    lt  lt     sTest1 length       lt  lt  sTest3 length    lt  lt  endl  return 0      The output of the example is this   C Style Results  Test1  ABCD  strlen    4     Test2             strlen    9 Test3  a     strlen    10  C   Style Results  Test1  ABCD  sTest1 size     4  sTest1 length    4 Test2             sTest2 size     9  sTest2 length    9 Test3  a     sTest3 size    10  sTest3 length    10

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If you re using a std  string  call length     std  string str    hello   std  cout  lt  lt  str  lt  lt       lt  lt  str length       Outputs  hello 5    If you re using a c-string  call strlen     const char  str    hello   std  cout  lt  lt  str  lt  lt       lt  lt  strlen str      Outputs  hello 5    Or  if you happen to like using Pascal-style strings  or f      strings as Joel Spolsky likes to call them when they have a trailing NULL   just dereference the first character   const char  str     005hello   std  cout  lt  lt  str   1  lt  lt       lt  lt   str     Outputs  hello 5

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If you re using old  C-style string instead of the newer  STL-style strings  there s the strlen function in the C run time library   const char  p    Hello   size t n   strlen p

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When dealing with C   strings  std  string   you re looking for length   or size    Both should provide you with the same value  However when dealing with C-Style strings  you would use strlen      include  lt iostream gt   include  lt string h gt   int main int argc  char   argv       std  string str    Hello       const char  otherstr    Hello       C-Style string    std  cout  lt  lt  str size    lt  lt  std  endl     std  cout  lt  lt  str length    lt  lt  std  endl     std  cout  lt  lt  strlen otherstr   lt  lt  std  endl     C way for string length    std  cout  lt  lt  strlen str c str     lt  lt  std  endl     convert C   string to C-string then call strlen    return 0      Output   6 6 6 6

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It might be the easiest way to input a string and find its length          Finding length of a string in C     include lt iostream gt   include lt string gt  using namespace std   int count string    int main     string str  cout  lt  lt   Enter a string     getline cin str   cout  lt  lt    nString     lt  lt  str  lt  lt  endl  cout  lt  lt  count str   lt  lt  endl   return 0      int count string s   if s          return 0  if s length      1    return 1  else     return  s length

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string foo      foo length          length and  size are synonymous  I just think that  length  is a slightly clearer word

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Simplest way to get length of string without bothering about std namespace is as follows   string with without spaces   include  lt iostream gt   include  lt string gt  using namespace std  int main        string str      getline cin str       cout lt  lt  Length of given string is  lt  lt str length        return 0      string without spaces   include  lt iostream gt   include  lt string gt  using namespace std  int main        string str      cin gt  gt str      cout lt  lt  Length of given string is  lt  lt str length        return 0

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For Unicode  Several answers here have addressed that  length   gives the wrong results with multibyte characters  but there are 11 answers and none of them have provided a solution   The case of Z      a        l            g        o               First of all  it s important to know what you mean by  length   For a motivating example  consider the string  Z      a        l            g        o                note that some languages  notably Thai  actually use combining diacritical marks  so this isn t just useful for 15-year-old memes  but obviously that s the most important use case   Assume it is encoded in UTF-8  There are 3 ways we can talk about the length of this string   95 bytes  00000000  5acd a5cd accc becd 89cc b3cc ba61 cc92  Z            a   00000010  cc92 cd8c cc8b cdaa ccb4 cd95 ccb2 6ccd                l  00000020  a4cc 80cc 9acc 88cd 9ccc a8cd 8ecc b0cc                   00000030  98cd 89cc 9f67 cc92 cd9d cd85 cd95 cd94       g           00000040  cca4 cd96 cc9f 6fcc 90cd afcc 9acc 85cd        o          00000050  aacc 86cd a3cc a1cc b5cc a1cc bccd 9a                      50 codepoints  LATIN CAPITAL LETTER Z COMBINING LEFT ANGLE BELOW COMBINING DOUBLE LOW LINE COMBINING INVERTED BRIDGE BELOW COMBINING LATIN SMALL LETTER I COMBINING LATIN SMALL LETTER R COMBINING VERTICAL TILDE LATIN SMALL LETTER A COMBINING TILDE OVERLAY COMBINING RIGHT ARROWHEAD BELOW COMBINING LOW LINE COMBINING TURNED COMMA ABOVE COMBINING TURNED COMMA ABOVE COMBINING ALMOST EQUAL TO ABOVE COMBINING DOUBLE ACUTE ACCENT COMBINING LATIN SMALL LETTER H LATIN SMALL LETTER L COMBINING OGONEK COMBINING UPWARDS ARROW BELOW COMBINING TILDE BELOW COMBINING LEFT TACK BELOW COMBINING LEFT ANGLE BELOW COMBINING PLUS SIGN BELOW COMBINING LATIN SMALL LETTER E COMBINING GRAVE ACCENT COMBINING DIAERESIS COMBINING LEFT ANGLE ABOVE COMBINING DOUBLE BREVE BELOW LATIN SMALL LETTER G COMBINING RIGHT ARROWHEAD BELOW COMBINING LEFT ARROWHEAD BELOW COMBINING DIAERESIS BELOW COMBINING RIGHT ARROWHEAD AND UP ARROWHEAD BELOW COMBINING PLUS SIGN BELOW COMBINING TURNED COMMA ABOVE COMBINING DOUBLE BREVE COMBINING GREEK YPOGEGRAMMENI LATIN SMALL LETTER O COMBINING SHORT STROKE OVERLAY COMBINING PALATALIZED HOOK BELOW COMBINING PALATALIZED HOOK BELOW COMBINING SEAGULL BELOW COMBINING DOUBLE RING BELOW COMBINING CANDRABINDU COMBINING LATIN SMALL LETTER X COMBINING OVERLINE COMBINING LATIN SMALL LETTER H COMBINING BREVE COMBINING LATIN SMALL LETTER A COMBINING LEFT ANGLE ABOVE   5 graphemes  Z with some s  t a with some s  t l with some s  t g with some s  t o with some s  t   Finding the lengths using ICU  There are C   classes for ICU  but they require converting to UTF-16  You can use the C types and macros directly to get some UTF-8 support    include  lt memory gt   include  lt iostream gt   include  lt unicode utypes h gt   include  lt unicode ubrk h gt   include  lt unicode utext h gt         C   helpers so we can use RAII       Note that ICU internally provides some C   wrappers  such as BreakIterator   however these only seem to work    for UTF-16 strings  and require transforming UTF-8 to UTF-16 before use     If you already have UTF-16 strings or can take the performance hit  you should probably use those instead of    the C functions  See  http   icu-project org apiref icu4c     struct UTextDeleter   void operator   UText  ptr    utext close ptr        struct UBreakIteratorDeleter   void operator   UBreakIterator  ptr    ubrk close ptr        using PUText   std  unique ptr lt UText  UTextDeleter gt   using PUBreakIterator   std  unique ptr lt UBreakIterator  UBreakIteratorDeleter gt    void checkStatus const UErrorCode status        if U FAILURE status                 throw std  runtime error u errorName status             size t countGraphemes UText  text           source for most of this  http   userguide icu-project org strings utext     UErrorCode status   U ZERO ERROR      PUBreakIterator it ubrk open UBRK CHARACTER   en us   nullptr  0   amp status        checkStatus status       ubrk setUText it get    text   amp status       checkStatus status       size t charCount   0      while ubrk next it get       UBRK DONE                  charCount            return charCount     size t countCodepoints UText  text        size t codepointCount   0      while UTEXT NEXT32 text     U SENTINEL                  codepointCount               reset the index so we can use the structure again     UTEXT SETNATIVEINDEX text  0       return codepointCount     void printStringInfo const std  string amp  utf8        UErrorCode status   U ZERO ERROR      PUText text utext openUTF8 nullptr  utf8 data    utf8 length     amp status        checkStatus status        std  cout  lt  lt   UTF-8 string  might look wrong if your console locale is different      lt  lt  utf8  lt  lt  std  endl      std  cout  lt  lt   Length  UTF-8 bytes      lt  lt  utf8 length    lt  lt  std  endl      std  cout  lt  lt   Length  UTF-8 codepoints      lt  lt  countCodepoints text get     lt  lt  std  endl      std  cout  lt  lt   Length  graphemes      lt  lt  countGraphemes text get     lt  lt  std  endl      std  cout  lt  lt  std  endl     void main int argc  char   argv        printStringInfo u8 Hello  world         printStringInfo u8                     printStringInfo u8  xF0 x9F x90 xBF        printStringInfo u8 Z      a        l            g        o                     This prints   UTF-8 string  might look wrong if your console locale is different   Hello  world  Length  UTF-8 bytes   13 Length  UTF-8 codepoints   13 Length  graphemes   13  UTF-8 string  might look wrong if your console locale is different                Length  UTF-8 bytes   36 Length  UTF-8 codepoints   12 Length  graphemes   10  UTF-8 string  might look wrong if your console locale is different    Length  UTF-8 bytes   4 Length  UTF-8 codepoints   1 Length  graphemes   1  UTF-8 string  might look wrong if your console locale is different   Z      a        l            g        o              Length  UTF-8 bytes   95 Length  UTF-8 codepoints   50 Length  graphemes   5   Boost Locale wraps ICU  and might provide a nicer interface  However  it still requires conversion to from UTF-16

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It depends on what string type you re talking about  There are many types of strings    const char  - a C-style multibyte string const wchar t  - a C-style wide string std  string - a  standard  multibyte string std  wstring - a  standard  wide string   For 3 and 4  you can use  size   or  length   methods   For 1  you can use strlen    but you must ensure that the string variable is not NULL      0   For 2  you can use wcslen    but you must ensure that the string variable is not NULL      0   There are other string types in non-standard C   libraries  such as MFC s CString  ATL s CComBSTR  ACE s ACE CString  and so on  with methods such as  GetLength    and so on  I can t remember the specifics of them all right off the top of my head   The STLSoft libraries have abstracted this all out with what they call string access shims  which can be used to get the string length  and other aspects  from any type  So for all of the above  including the non-standard library ones  using the same function stlsoft  c str len    This article describes how it all works  as it s not all entirely obvious or easy

[c++] How to get the number of characters in a std::string?

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