Alternative to itoa for converting integer to string C

Question

I was wondering if there was an alternative to itoa   for converting an integer to a string because when I run it in visual Studio I get warnings  and when I try to build my program under Linux  I get a compilation error

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Behind the scenes  lexical cast does this   std  stringstream str  str  lt  lt  myint  std  string result  str  gt  gt  result    If you don t want to  drag in  boost for this  then using the above is a good solution

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boost  lexical cast works pretty well    include  lt boost lexical cast hpp gt  int main int argc  char   argv        std  string foo   boost  lexical cast lt std  string gt  argc

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The best answer  IMO  is the function provided here   http   www jb man ac uk  slowe cpp itoa html  It mimics the non-ANSI function provided by many libs   char  itoa int value  char  result  int base     It s also lightning fast and optimizes well under -O3  and the reason you re not using c   string format       or sprintf is that they are too slow  right

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Try sprintf     char str 12   int num   3  sprintf str    d   num      str now contains  3    sprintf   is like printf   but outputs to a string   Also  as Parappa mentioned in the comments  you might want to use snprintf   to stop a buffer overflow from occuring  where the number you re converting doesn t fit the size of your string   It works like this   snprintf str  sizeof str     d   num

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Most of the above suggestions technically aren t C    they re C solutions   Look into the use of std  stringstream

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You can actually convert anything to a string with one cleverly written template function  This code example uses a loop to create subdirectories in a Win-32 system  The string concatenation operator  operator   is used to concatenate a root with a suffix to generate directory names  The suffix is created by converting the loop control variable  i  to a C   string  using the template function  and concatenating that with another string     Mark Renslow  Globe University  Minnesota School of Business  Utah Career College   C   instructor and Network Dean of Information Technology   include  lt cstdlib gt   include  lt iostream gt   include  lt string gt   include  lt sstream gt     string stream  include  lt direct h gt   using namespace std   string intToString int x                                                This function is similar to itoa          integer to alpha   a non-standard       C language function  It takes an         integer as input and as output           returns a C   string                     itoa    returned a C-string  null-       terminated                               This function is not needed because      the following template function          does it all                                                                              string r         stringstream s          s  lt  lt  x         r   s str            return r      template  lt class T gt  string toString  T argument                                                This template shows the power of         C   templates  This function will        convert anything to a string             Precondition                             operator lt  lt  is defined for type T                                                       string r         stringstream s          s  lt  lt  argument         r   s str            return r      int main          string s       cout  lt  lt   What directory would you like me to make         cin  gt  gt  s       try             mkdir s c str               catch  exception amp  e               cerr  lt  lt  e what     lt  lt  endl             chdir s c str            Using a loop and string concatenation to make several sub-directories     for int i   0  i  lt  10  i                  s    Dir            s   s   toString i           mkdir s c str               system  PAUSE        return EXIT SUCCESS

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Archeology itoa was a non-standard helper function designed to complement the atoi standard function  and probably hiding a sprintf  Most its features can be implemented in terms of sprintf   http   www cplusplus com reference clibrary cstdlib itoa html The C Way Use sprintf  Or snprintf  Or whatever tool you find  Despite the fact some functions are not in the standard  as rightly mentioned by  quot onebyone quot  in one of his comments  most compiler will offer you an alternative  e g  Visual C   has its own  snprintf you can typedef to snprintf if you need it   The C   way  Use the C   streams  in the current case std  stringstream  or even the deprecated std  strstream  as proposed by Herb Sutter in one of his books  because it s somewhat faster   Conclusion You re in C    which means that you can choose the way you want it   The faster way  i e  the C way   but you should be sure the code is a bottleneck in your application  premature optimizations are evil  etc   and that your code is safely encapsulated to avoid risking buffer overruns   The safer way  i e   the C   way   if you know this part of the code is not critical  so better be sure this part of the code won t break at random moments because someone mistook a size or a pointer  which happens in real life  like    yesterday  on my computer  because someone thought it  quot cool quot  to use the faster way without really needing it

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int number   123   stringstream   s   s  lt  lt  number   cout  lt  lt  ss str    lt  lt  endl

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Try sprintf     char str 12   int num   3  sprintf str    d   num      str now contains  3    sprintf   is like printf   but outputs to a string   Also  as Parappa mentioned in the comments  you might want to use snprintf   to stop a buffer overflow from occuring  where the number you re converting doesn t fit the size of your string   It works like this   snprintf str  sizeof str     d   num

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int number   123   stringstream   s   s  lt  lt  number   cout  lt  lt  ss str    lt  lt  endl

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Note that all of the stringstream methods may involve locking around the use of the locale  object for formatting  This may be something to be wary of if you re using this conversion from multiple threads     See here for more  Convert a number to a string with specified length in C

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In C  11 you can use std  to string    include  lt string gt   std  string s   std  to string 5     If you re working with prior to C  11  you could use C   streams    include  lt sstream gt   int i   5  std  string s  std  stringstream out  out  lt  lt  i  s   out str      Taken from http   notfaq wordpress com 2006 08 30 c-convert-int-to-string

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Try sprintf     char str 12   int num   3  sprintf str    d   num      str now contains  3    sprintf   is like printf   but outputs to a string   Also  as Parappa mentioned in the comments  you might want to use snprintf   to stop a buffer overflow from occuring  where the number you re converting doesn t fit the size of your string   It works like this   snprintf str  sizeof str     d   num

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11 finally resolves this providing std  to string  Also boost  lexical cast is handy tool for older compilers

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I wrote this thread-safe function some time ago  and am very happy with the results and feel the algorithm is lightweight and lean  with performance that is about 3X the standard MSVC  itoa   function    Here s the link  Optimal Base-10 only itoa   function  Performance is at least 10X that of sprintf    The benchmark is also the function s QA test  as follows    start   clock    for  int i   LONG MIN  i  lt  LONG MAX  i          if  i    atoi  i32toa buff   int32 t i              printf   nError for  i   i             if   i  printf   nAt zero      printf   nElapsed time was  f milliseconds    double clock   -  double  start      There are some silly suggestions made about using the caller s storage that would leave the result floating somewhere in a buffer in the caller s address space  Ignore them  The code I listed works perfectly  as the benchmark QA code demonstrates    I believe this code is lean enough to use in an embedded environment  YMMV  of course

User · Answer

11 finally resolves this providing std  to string  Also boost  lexical cast is handy tool for older compilers

User · Answer

On Windows CE derived platforms  there are no iostreams by default  The way to go there is preferaby with the  itoa lt  gt  family  usually  itow lt  gt   since most string stuff are Unicode there anyway

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If you are interested in fast as well as safe integer to string conversion method and not limited to the standard library  I can recommend the format int method from the  fmt  library   fmt  format int 42  str         convert to std  string fmt  format int 42  c str       convert and get as a C string                                  mind the lifetime  same as std  string  c str      According to the integer to string conversion benchmarks from Boost Karma  this method several times faster than glibc s sprintf or std  stringstream  It is even faster than Boost Karma s own int generator as was confirm by an independent benchmark   Disclaimer  I m the author of this library

User · Answer

Behind the scenes  lexical cast does this   std  stringstream str  str  lt  lt  myint  std  string result  str  gt  gt  result    If you don t want to  drag in  boost for this  then using the above is a good solution

User · Answer

boost  lexical cast works pretty well    include  lt boost lexical cast hpp gt  int main int argc  char   argv        std  string foo   boost  lexical cast lt std  string gt  argc

User · Answer

On Windows CE derived platforms  there are no iostreams by default  The way to go there is preferaby with the  itoa lt  gt  family  usually  itow lt  gt   since most string stuff are Unicode there anyway

User · Answer

Allocate a string of sufficient length  then use snprintf

User · Answer

boost  lexical cast works pretty well    include  lt boost lexical cast hpp gt  int main int argc  char   argv        std  string foo   boost  lexical cast lt std  string gt  argc

User · Answer

Archeology itoa was a non-standard helper function designed to complement the atoi standard function  and probably hiding a sprintf  Most its features can be implemented in terms of sprintf   http   www cplusplus com reference clibrary cstdlib itoa html The C Way Use sprintf  Or snprintf  Or whatever tool you find  Despite the fact some functions are not in the standard  as rightly mentioned by  quot onebyone quot  in one of his comments  most compiler will offer you an alternative  e g  Visual C   has its own  snprintf you can typedef to snprintf if you need it   The C   way  Use the C   streams  in the current case std  stringstream  or even the deprecated std  strstream  as proposed by Herb Sutter in one of his books  because it s somewhat faster   Conclusion You re in C    which means that you can choose the way you want it   The faster way  i e  the C way   but you should be sure the code is a bottleneck in your application  premature optimizations are evil  etc   and that your code is safely encapsulated to avoid risking buffer overruns   The safer way  i e   the C   way   if you know this part of the code is not critical  so better be sure this part of the code won t break at random moments because someone mistook a size or a pointer  which happens in real life  like    yesterday  on my computer  because someone thought it  quot cool quot  to use the faster way without really needing it

User · Answer

Most of the above suggestions technically aren t C    they re C solutions   Look into the use of std  stringstream

User · Answer

Allocate a string of sufficient length  then use snprintf

User · Answer

Archeology itoa was a non-standard helper function designed to complement the atoi standard function  and probably hiding a sprintf  Most its features can be implemented in terms of sprintf   http   www cplusplus com reference clibrary cstdlib itoa html The C Way Use sprintf  Or snprintf  Or whatever tool you find  Despite the fact some functions are not in the standard  as rightly mentioned by  quot onebyone quot  in one of his comments  most compiler will offer you an alternative  e g  Visual C   has its own  snprintf you can typedef to snprintf if you need it   The C   way  Use the C   streams  in the current case std  stringstream  or even the deprecated std  strstream  as proposed by Herb Sutter in one of his books  because it s somewhat faster   Conclusion You re in C    which means that you can choose the way you want it   The faster way  i e  the C way   but you should be sure the code is a bottleneck in your application  premature optimizations are evil  etc   and that your code is safely encapsulated to avoid risking buffer overruns   The safer way  i e   the C   way   if you know this part of the code is not critical  so better be sure this part of the code won t break at random moments because someone mistook a size or a pointer  which happens in real life  like    yesterday  on my computer  because someone thought it  quot cool quot  to use the faster way without really needing it

User · Answer

Note that all of the stringstream methods may involve locking around the use of the locale  object for formatting  This may be something to be wary of if you re using this conversion from multiple threads     See here for more  Convert a number to a string with specified length in C

User · Answer

The best answer  IMO  is the function provided here   http   www jb man ac uk  slowe cpp itoa html  It mimics the non-ANSI function provided by many libs   char  itoa int value  char  result  int base     It s also lightning fast and optimizes well under -O3  and the reason you re not using c   string format       or sprintf is that they are too slow  right

User · Answer

You can actually convert anything to a string with one cleverly written template function  This code example uses a loop to create subdirectories in a Win-32 system  The string concatenation operator  operator   is used to concatenate a root with a suffix to generate directory names  The suffix is created by converting the loop control variable  i  to a C   string  using the template function  and concatenating that with another string     Mark Renslow  Globe University  Minnesota School of Business  Utah Career College   C   instructor and Network Dean of Information Technology   include  lt cstdlib gt   include  lt iostream gt   include  lt string gt   include  lt sstream gt     string stream  include  lt direct h gt   using namespace std   string intToString int x                                                This function is similar to itoa          integer to alpha   a non-standard       C language function  It takes an         integer as input and as output           returns a C   string                     itoa    returned a C-string  null-       terminated                               This function is not needed because      the following template function          does it all                                                                              string r         stringstream s          s  lt  lt  x         r   s str            return r      template  lt class T gt  string toString  T argument                                                This template shows the power of         C   templates  This function will        convert anything to a string             Precondition                             operator lt  lt  is defined for type T                                                       string r         stringstream s          s  lt  lt  argument         r   s str            return r      int main          string s       cout  lt  lt   What directory would you like me to make         cin  gt  gt  s       try             mkdir s c str               catch  exception amp  e               cerr  lt  lt  e what     lt  lt  endl             chdir s c str            Using a loop and string concatenation to make several sub-directories     for int i   0  i  lt  10  i                  s    Dir            s   s   toString i           mkdir s c str               system  PAUSE        return EXIT SUCCESS

User · Answer

I use these templates  template  lt typename T gt  string toStr T tmp        ostringstream out      out  lt  lt  tmp      return out str        template  lt typename T gt  T strTo string tmp        T output      istringstream in tmp       in  gt  gt  output      return output

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In C  11 you can use std  to string    include  lt string gt   std  string s   std  to string 5     If you re working with prior to C  11  you could use C   streams    include  lt sstream gt   int i   5  std  string s  std  stringstream out  out  lt  lt  i  s   out str      Taken from http   notfaq wordpress com 2006 08 30 c-convert-int-to-string

User · Answer

In C  11 you can use std  to string    include  lt string gt   std  string s   std  to string 5     If you re working with prior to C  11  you could use C   streams    include  lt sstream gt   int i   5  std  string s  std  stringstream out  out  lt  lt  i  s   out str      Taken from http   notfaq wordpress com 2006 08 30 c-convert-int-to-string

User · Answer

Most of the above suggestions technically aren t C    they re C solutions   Look into the use of std  stringstream

User · Answer

Try Boost Format or FastFormat  both high-quality C   libraries   int i   10  std  string result    WIth Boost Format  result   str boost  format   1    i      or FastFormat  fastformat  fmt result    0    i   fastformat  write result  i     Obviously they both do a lot more than a simple conversion of a single integer

User · Answer

Most of the above suggestions technically aren t C    they re C solutions   Look into the use of std  stringstream

User · Answer

On Windows CE derived platforms  there are no iostreams by default  The way to go there is preferaby with the  itoa lt  gt  family  usually  itow lt  gt   since most string stuff are Unicode there anyway

User · Answer

We can define our own iota function in c   as   string itoa int a        string ss         create empty string     while a                int x a 10          a  10          char i  0           i i x          ss i ss         append new character at the front of the string            return ss      Don t forget to  include  lt string gt

User · Answer

Behind the scenes  lexical cast does this   std  stringstream str  str  lt  lt  myint  std  string result  str  gt  gt  result    If you don t want to  drag in  boost for this  then using the above is a good solution

User · Answer

We can define our own iota function in c   as   string itoa int a        string ss         create empty string     while a                int x a 10          a  10          char i  0           i i x          ss i ss         append new character at the front of the string            return ss      Don t forget to  include  lt string gt

User · Answer

In C  11 you can use std  to string    include  lt string gt   std  string s   std  to string 5     If you re working with prior to C  11  you could use C   streams    include  lt sstream gt   int i   5  std  string s  std  stringstream out  out  lt  lt  i  s   out str      Taken from http   notfaq wordpress com 2006 08 30 c-convert-int-to-string

User · Answer

I wrote this thread-safe function some time ago  and am very happy with the results and feel the algorithm is lightweight and lean  with performance that is about 3X the standard MSVC  itoa   function    Here s the link  Optimal Base-10 only itoa   function  Performance is at least 10X that of sprintf    The benchmark is also the function s QA test  as follows    start   clock    for  int i   LONG MIN  i  lt  LONG MAX  i          if  i    atoi  i32toa buff   int32 t i              printf   nError for  i   i             if   i  printf   nAt zero      printf   nElapsed time was  f milliseconds    double clock   -  double  start      There are some silly suggestions made about using the caller s storage that would leave the result floating somewhere in a buffer in the caller s address space  Ignore them  The code I listed works perfectly  as the benchmark QA code demonstrates    I believe this code is lean enough to use in an embedded environment  YMMV  of course

User · Answer

Note that all of the stringstream methods may involve locking around the use of the locale  object for formatting  This may be something to be wary of if you re using this conversion from multiple threads     See here for more  Convert a number to a string with specified length in C

User · Answer

Allocate a string of sufficient length  then use snprintf

User · Answer

Note that all of the stringstream methods may involve locking around the use of the locale  object for formatting  This may be something to be wary of if you re using this conversion from multiple threads     See here for more  Convert a number to a string with specified length in C

User · Answer

boost  lexical cast works pretty well    include  lt boost lexical cast hpp gt  int main int argc  char   argv        std  string foo   boost  lexical cast lt std  string gt  argc

User · Answer

On Windows CE derived platforms  there are no iostreams by default  The way to go there is preferaby with the  itoa lt  gt  family  usually  itow lt  gt   since most string stuff are Unicode there anyway

User · Answer

Archeology itoa was a non-standard helper function designed to complement the atoi standard function  and probably hiding a sprintf  Most its features can be implemented in terms of sprintf   http   www cplusplus com reference clibrary cstdlib itoa html The C Way Use sprintf  Or snprintf  Or whatever tool you find  Despite the fact some functions are not in the standard  as rightly mentioned by  quot onebyone quot  in one of his comments  most compiler will offer you an alternative  e g  Visual C   has its own  snprintf you can typedef to snprintf if you need it   The C   way  Use the C   streams  in the current case std  stringstream  or even the deprecated std  strstream  as proposed by Herb Sutter in one of his books  because it s somewhat faster   Conclusion You re in C    which means that you can choose the way you want it   The faster way  i e  the C way   but you should be sure the code is a bottleneck in your application  premature optimizations are evil  etc   and that your code is safely encapsulated to avoid risking buffer overruns   The safer way  i e   the C   way   if you know this part of the code is not critical  so better be sure this part of the code won t break at random moments because someone mistook a size or a pointer  which happens in real life  like    yesterday  on my computer  because someone thought it  quot cool quot  to use the faster way without really needing it

User · Answer

Allocate a string of sufficient length  then use snprintf

User · Answer

Behind the scenes  lexical cast does this   std  stringstream str  str  lt  lt  myint  std  string result  str  gt  gt  result    If you don t want to  drag in  boost for this  then using the above is a good solution

User · Answer

I use these templates  template  lt typename T gt  string toStr T tmp        ostringstream out      out  lt  lt  tmp      return out str        template  lt typename T gt  T strTo string tmp        T output      istringstream in tmp       in  gt  gt  output      return output

User · Answer

If you are interested in fast as well as safe integer to string conversion method and not limited to the standard library  I can recommend the format int method from the  fmt  library   fmt  format int 42  str         convert to std  string fmt  format int 42  c str       convert and get as a C string                                  mind the lifetime  same as std  string  c str      According to the integer to string conversion benchmarks from Boost Karma  this method several times faster than glibc s sprintf or std  stringstream  It is even faster than Boost Karma s own int generator as was confirm by an independent benchmark   Disclaimer  I m the author of this library

User · Answer

Try sprintf     char str 12   int num   3  sprintf str    d   num      str now contains  3    sprintf   is like printf   but outputs to a string   Also  as Parappa mentioned in the comments  you might want to use snprintf   to stop a buffer overflow from occuring  where the number you re converting doesn t fit the size of your string   It works like this   snprintf str  sizeof str     d   num

User · Answer

Try Boost Format or FastFormat  both high-quality C   libraries   int i   10  std  string result    WIth Boost Format  result   str boost  format   1    i      or FastFormat  fastformat  fmt result    0    i   fastformat  write result  i     Obviously they both do a lot more than a simple conversion of a single integer

[c++] Alternative to itoa() for converting integer to string C++?

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