Easiest way to convert int to string in C

Question

What is the easiest way to convert from int to equivalent string in C     I am aware of two methods  Is there any easier way    1   int a   10  char  intStr   itoa a   string str   string intStr      2   int a   10  stringstream ss  ss  lt  lt  a  string str   ss str

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If you have Boost installed  which you should     include  lt boost lexical cast hpp gt   int num   4  std  string str   boost  lexical cast lt std  string gt  num

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You use a counter type of algorithm to convert to a string  I got this technique from programming Commodore 64 computers  It is also good for game programming    You take the integer and take each digit that is weighted by powers of 10  So assume the integer is 950    If the integer equals or is greater than 100 000 then subtract 100 000 and increase the counter in the string at   000000     keep doing it until no more numbers in position 100 000  Drop another power of ten  If the integer equals or is greater than 10 000 then subtract 10 000 and increase the counter in the string at   000000     1 position   keep doing it until no more numbers in position 10 000   Drop another power of ten Repeat the pattern   I know 950 is too small to use as an example  but I hope you get the idea

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Current C   Starting with C  11  there s a std  to string function overloaded for integer types  so you can use code like  int a   20  std  string s   std  to string a      or  auto s   std  to string a    The standard defines these as being equivalent to doing the conversion with sprintf  using the conversion specifier that matches the supplied type of object  such as  d for int   into a buffer of sufficient size  then creating an std  string of the contents of that buffer  Old C   For older  pre-C  11  compilers  probably the most common easy way wraps essentially your second choice into a template that s usually named lexical cast  such as the one in Boost  so your code looks like this  int a   10  string s   lexical cast lt string gt  a    One nicety of this is that it supports other casts as well  e g   in the opposite direction works just as well   Also note that although Boost lexical cast started out as just writing to a stringstream  then extracting back out of the stream  it now has a couple of additions  First of all  specializations for quite a few types have been added  so for many common types  it s substantially faster than using a stringstream  Second  it now checks the result  so  for example  if you convert from a string to an int  it can throw an exception if the string contains something that couldn t be converted to an int  e g   1234 would succeed  but 123abc would throw

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Not that I know of  in pure C    But a little modification of what you mentioned  string s   string itoa a      should work  and it s pretty short

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Picking up a discussion with  v oddou a couple of years later  C  17 has finally delivered a way to do the originally macro-based type-agnostic solution  preserved below  without going through macro uglyness     variadic template template  lt  typename    Args  gt  std  string sstr  Args  amp  amp     args         std  ostringstream sstr         fold expression       sstr  lt  lt  std  dec  lt  lt       lt  lt  args        return sstr str       Usage  int i   42  std  string s   sstr   quot i is   quot   i    puts  sstr  i   c str       Foo x  42    throw std  runtime error  sstr   quot Foo is   quot   x   quot    i is  quot   i        Original answer  Since  quot converting     to string quot  is a recurring problem  I always define the SSTR   macro in a central header of my C   sources   include  lt sstream gt    define SSTR  x   static cast lt  std  ostringstream  amp   gt               std  ostringstream    lt  lt  std  dec  lt  lt  x     str    Usage is as easy as could be  int i   42  std  string s   SSTR   quot i is   quot   lt  lt  i    puts  SSTR  i   c str       Foo x  42    throw std  runtime error  SSTR   quot Foo is   quot   lt  lt  x  lt  lt   quot    i is  quot   lt  lt  i       The above is C  98 compatible  if you cannot use C  11 std  to string   and does not need any third-party includes  if you cannot use Boost lexical cast lt  gt    both these other solutions have a better performance though

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C  11 introduces std  stoi  and variants for each numeric type  and std  to string  the counterparts of the C atoi and itoa but expressed in term of std  string    include  lt string gt    std  string s   std  to string 42     is therefore the shortest way I can think of  You can even omit naming the type  using the auto keyword   auto s   std  to string 42     Note  see  string conversions   21 5 in n3242

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int i   255  std  string s   std  to string i    In c    to string   will create a string object of the integer value by representing the value as a sequence of characters

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I usually use the following method    include  lt sstream gt   template  lt typename T gt    std  string NumberToString   T Number            std  ostringstream ss       ss  lt  lt  Number       return ss str          It is described in details here

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Use    define convertToString x   x  int main         convertToString 42      Returns const char  equivalent of 42

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char   bufSecs   new char 32   char   bufMs   new char 32   sprintf bufSecs    d   timeStart elapsed   1000   sprintf bufMs    d   timeStart elapsed   1000

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Here s another easy way to do   char str 100   sprintf str    d   101   string s   str    sprintf is a well-known one to insert any data into a string of the required format   You can convert a char   array to a string as shown in the third line

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First include    include  lt string gt   include  lt sstream gt    Second add the method   template  lt typename T gt  string NumberToString T pNumber     ostringstream oOStrStream   oOStrStream  lt  lt  pNumber   return oOStrStream str        Use the method like this   NumberToString 69     or  int x   69  string vStr   NumberToString x      Hello word

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For C  98  there s a few options   boost lexical cast  Boost is not a part of the C   library  but contains many useful library extensions      The lexical cast function template offers a convenient and consistent form for supporting common conversions to and from arbitrary types when they are represented as text      -- Boost s Documentation     include  boost lexical cast hpp   include  lt string gt   int main         int x   5      std  string x str   boost  lexical cast lt std  string gt  x       return 0      As for runtime  the lexical cast operation takes about 80 microseconds  on my machine  on the first conversion  and then speeds up considerably afterwards if done redundantly     itoa     This function is not defined in ANSI-C and is not part of C    but is supported by some compilers     -- cplusplus com   This means that gcc g   cannot compile code using itoa    include  lt stdlib h gt   int main         int x   5      char   x str   new char 2       x str   itoa x  x str  10      base 10     return 0      No runtime to report  I don t have Visual Studio installed  which is reportedly able to compile itoa     sprintf  sprintf is a C standard library function that works on C strings  and is a perfectly valid alternative      Composes a string with the same text that would be printed if format was used on printf  but instead of being printed  the content is stored as a C string in the buffer pointed by str     -- cplusplus com    include  lt stdio h gt   int main         int x   5      char   x str   new char 2       int chars written   sprintf x str    d   x       return 0      The stdio h header may not be necessary  As for runtime  the sprintf operation takes about 40 microseconds  on my machine  on the first conversion  and then speeds up considerably afterwards if done redundantly     stringstream  This is the C   library s main way of converting integers to strings  and vice versa  There are similar sister functions to stringstream that further limit the intended use of the stream  such as ostringstream  Using ostringstream specifically tells the reader of your code that you only intend to use the  lt  lt  operator  essentially  This function is all that s particularly necessary to convert an integer to a string  See this question for a more elaborate discussion    include  lt sstream gt   include  lt string gt   int main         int x   5      std  ostringstream stream      stream  lt  lt  x      std  string x str   stream str        return 0      As for runtime  the ostringstream operation takes about 71 microseconds  on my machine   and then speeds up considerably afterwards if done redundantly  but not by as much as the previous functions     Of course there are other options  and you can even wrap one of these into your own function  but this offers an analytical look at some of the popular ones

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string number to string int x         if   x          return  0        string s  s2      while x            s push back x 10    0            x    10            reverse s begin    s end         return s

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If you re using MFC  you can use CString   int a   10  CString strA  strA Format   d   a

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It would be easier using stringstreams    include  lt sstream gt   int x   42              The integer string str              The string ostringstream temp       temp  as in temporary temp  lt  lt  x  str   temp str          str is  temp  as string   Or make a function    include  lt sstream gt   string IntToString int a        ostringstream temp      temp  lt  lt  a      return temp str

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Using the plain standard stdio header  you can cast the integer over sprintf into a buffer  like so   include  lt stdio h gt  int main         int x 23    char y 2     the output buffer   sprintf y  quot  d quot  x     printf  quot  s quot  y       Remember to take care of your buffer size according to your needs  the string output size

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I use   int myint   0  long double myLD   0 0   string myint str   static cast lt ostringstream  gt   amp  ostringstream    lt  lt  myint  - gt str    string myLD str   static cast lt ostringstream  gt   amp  ostringstream    lt  lt  myLD  - gt str      It works on my Windows and Linux g   compilers

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namespace std       inline string to string int  Val             Convert long long to string         char  Buf 2    MAX INT DIG           snprintf  Buf    d    Val           return  string  Buf              You can now use to string 5

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This worked for me -  My code    include  lt iostream gt  using namespace std   int main         int n   32      string s   to string n       cout  lt  lt   string      s   lt  lt  endl      return 0

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sprintf   is pretty good for format conversion  You can then assign the resulting C string to the C   string as you did in 1

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Use   include lt iostream gt   include lt string gt   std  string intToString int num    int main         int integer   4782151       std  string integerAsStr   intToString integer        std  cout  lt  lt   quot integer    quot   lt  lt  integer  lt  lt  std  endl      std  cout  lt  lt   quot integerAsStr    quot   lt  lt  integerAsStr  lt  lt  std  endl       return 0     std  string intToString int num        std  string numAsStr      bool isNegative   num  lt  0      if isNegative  num  -1       do              char toInsert    num   10    48         numAsStr insert 0  1  toInsert           num    10       while  num          return isNegative  numAsStr insert 0  1   -     numAsStr

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Using stringstream for number conversion is dangerous   See http   www cplusplus com reference ostream ostream operator 3C 3C  where it tells that operator lt  lt  inserts formatted output   Depending on your current locale an integer greater than 3 digits  could convert to a string of 4 digits  adding an extra thousands separator   E g   int   1000 could be convertet to a string 1 001  This could make comparison operations not work at all   So I would strongly recommend using the std  to string way  It is easier and does what you expect   Updated  see comments below       C  17 provides std  to chars as a higher-performance   locale-independent alternative

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You can use std  to string available in C  11 as suggested by Matthieu M   std  to string 42    Or  if performance is critical  for example  if you do lots of conversions   you can use fmt  format int from the  fmt  library to convert an integer to std  string  fmt  format int 42  str     Or a C string  fmt  format int f 42   f c str     The latter doesn t do any dynamic memory allocations and is more than 70  faster than std  to string on Boost Karma benchmarks  See Converting a hundred million integers to strings per second for more details  Note that both are thread-safe  Unlike std  to string  fmt  format int doesn t require C  11 and works with any C   compiler  Disclaimer  I m the author of the  fmt  library

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It s rather easy to add some syntactical sugar that allows one to compose strings on the fly in a stream-like way   include  lt string gt   include  lt sstream gt   struct strmake       std  stringstream s      template  lt typename T gt  strmake amp  operator  lt  lt   const T amp  x            s  lt  lt  x  return  this               operator std  string    return s str          Now you may append whatever you want  provided that an operator  lt  lt   std  ostream amp      is defined for it  to strmake   and use it in place of an std  string   Example    include  lt iostream gt   int main         std  string x         strmake    lt  lt   Current time is    lt  lt  5 5  lt  lt       lt  lt  5 5  lt  lt    GST       std  cout  lt  lt  x  lt  lt  std  endl

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C  11 introduced std  to string   for numeric types   int n   123     Input  signed unsigned short int long long long float double std  string str   std  to string n      Output  std  string

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C  17 provides std  to chars as a higher-performance locale-independent alternative

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I think using stringstream is pretty easy    string toString int n          stringstream ss n        ss  lt  lt  n       return ss str         int main          int n      cin  gt  gt  n      cout  lt  lt  toString n   lt  lt  endl      return 0

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EDITED  If you need fast conversion of an integer with a fixed number of digits to char  left-padded with  0   this is the example for little-endian architectures  all x86  x86 64 and others    If you are converting a two-digit number   int32 t s   0x3030    n 10     n 10   lt  lt  8    If you are converting a three-digit number   int32 t s   0x303030    n 100     n 10 10   lt  lt  8    n 10   lt  lt  16    If you are converting a four-digit number   int64 t s   0x30303030    n 1000     n 100 10  lt  lt 8    n 10 10  lt  lt 16    n 10  lt  lt 24    And so on up to seven-digit numbers  In this example n is a given integer  After conversion it s string representation can be accessed as  char   amp s   std  cout  lt  lt   char   amp s  lt  lt  std  endl    NOTE  If you need it on big-endian byte order  though I did not tested it  but here is an example  for three-digit number it is int32 t s   0x00303030    n 100  lt  lt  24    n 10 10  lt  lt 16    n 10  lt  lt 8  for four-digit numbers  64 bit arch   int64 t s   0x0000000030303030    n 1000  lt  lt 56    n 100 10  lt  lt 48    n 10 10  lt  lt 40    n 10  lt  lt 32  I think it should work

[c++] Easiest way to convert int to string in C++

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