Converting int to string in C

Question

I am using the itoa   function to convert an int into string  but it is giving an error   undefined reference to  itoa  collect2  ld returned 1 exit status   What is the reason  Is there some other way to perform this conversion

User · Answer

see this example   include  lt stdlib h gt     for itoa   call  include  lt stdio h gt     int main         int num   145      char buf 5           convert 123 to string  buf      itoa num  buf  10           print our string     printf   s n   buf        return 0      see this link having other examples

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Similar implementation to Ahmad Sirojuddin but slightly different semantics  From a security perspective  any time a function writes into a string buffer  the function should really  know  the size of the buffer and refuse to write past the end of it  I would guess its a part of the reason you can t find itoa anymore   Also  the following implementation avoids performing the module devide operation twice   char  u32todec  uint32 t    value                  char         buf                  int         size        if size  gt  1           int i size-1  offset  bytes          buf i--    0           do              buf i--   value   10   0               value   value 10           while  value  gt  0   amp  amp   i gt  0            offset i 1          if offset  gt  0               bytes size-i-1              for i 0 i lt bytes i                    buf i  buf i offset                     return buf       else         return NULL      The following code both tests the above code and demonstrates its correctness   int main void        uint64 t acc      uint32 t inc      char buf 16       size t bufsize      for acc 0  inc 7  acc lt 0x100000000  acc  inc           printf   u      uint32 t acc           for bufsize 17  bufsize gt 0  bufsize  2               if NULL    u32todec  uint32 t acc  buf  bufsize                   printf   s    buf                     printf   n            if acc inc  gt  9              inc  7            return 0

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Use snprintf - it is standard an available in every compilator  Query it for the size needed by calling it with NULL  0 parameters  Allocate one character more for null at the end   int length   snprintf  NULL  0    d   x    char  str   malloc  length   1    snprintf  str  length   1    d   x        free str

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Better use sprintf      char stringNum 20   int num 100  sprintf stringNum   d  num

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Like Edwin suggested  use snprintf    include  lt stdio h gt  int main int argc  const char  argv          int n   1234      char buf 10       snprintf buf  10    d   n       printf   s n   buf       return 0

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void itos int value  char  str  size t size        snprintf str  size    d   value         works with call by reference  Use it like this e g    int someIntToParse  char resultingString length someIntToParse     itos someIntToParse  resultingString  length someIntToParse      now resultingString will hold your C- string

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Use snprintf  it is more portable than itoa   itoa is not part of standard C  nor is it part of standard C    but  a lot of compilers and associated libraries support it   Example of sprintf  char  buffer       allocate a buffer     int value   4564  sprintf buffer    d   value     Example of snprintf  char buffer 10   int value   234452  snprintf buffer  10    d   value     Both functions are similar to fprintf  but output is written into an array rather than to a stream  The difference between sprintf and snprintf is that snprintf guarantees no buffer overrun by writing up to a maximum number of characters that can be stored in the buffer

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Before I continue  I must warn you that itoa is NOT an ANSI function     it s not a standard C function  You should use sprintf to convert an int into a string   itoa takes three arguments    The first one is the integer to be converted  The second is a pointer to an array of characters - this is where the string is going to be stored  The program may crash if you pass in a char   variable  so you should pass in a normal sized char array and it will work fine  The last one is NOT the size of the array  but it s the BASE of your number - base 10 is the one you re most likely to use    The function returns a pointer to its second argument     where it has stored the converted string   itoa is a very useful function  which is supported by some compilers - it s a shame it isn t support by all  unlike atoi   If you still want to use itoa  here is how should you use it   Otherwise  you have another option using sprintf  as long as you want base 8  10 or 16 output    char str 5   printf  15 in binary is  s n    itoa 15  str  2

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char string something   sprintf string    d   42

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If you really want to use itoa  you need to include the standard library header    include  lt stdlib h gt    I also believe that if you re on Windows  using MSVC   then itoa is actually  itoa   See http   msdn microsoft com en-us library yakksftt v VS 100  aspx  Then again  since you re getting a message from collect2  you re likely running GCC on  nix

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Usually snprintf   is the way to go   char str 16      could be less but i m too lazy to look for the actual the max length of an integer snprintf str  sizeof str     d   your integer

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You can make your own itoa  with this function   void my utoa int dataIn  char  bffr  int radix   int temp dataIn  temp dataIn   dataIn  int stringLen 1   while   int temp dataIn radix    0       temp dataIn    int temp dataIn radix      stringLen        printf  stringLen    d n   stringLen   temp dataIn   dataIn  do        bffr stringLen-1     temp dataIn radix   0       temp dataIn    int  temp dataIn   radix   while stringLen--      and this is example   char buffer 33   int main      my utoa 54321  buffer  10     printf buffer     printf   n       my utoa 13579  buffer  10     printf buffer     printf   n

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itoa   function is not defined in ANSI-C  so not implemented by default for some platforms  Reference Link   s n printf   functions are easiest replacement of itoa    However itoa  integer to ascii  function can be used as a better overall solution of integer to ascii conversion problem  itoa   is also better than s n printf   as performance depending on the implementation  A reduced itoa  support only 10 radix  implementation as an example  Reference Link Another complete itoa   implementation is below  Reference Link    include  lt stdbool h gt    include  lt string h gt      A utility function to reverse a string  char  reverse char  str      char  p1   p2     if    str       str          return str    for  p1   str  p2   str   strlen str  - 1  p2  gt  p1    p1  --p2               p1     p2           p2     p1           p1     p2        return str       Implementation of itoa    char  itoa int num  char  str  int base          int i   0       bool isNegative   false             Handle 0 explicitely  otherwise empty string is printed for 0        if  num    0                  str i       0            str i      0            return str                    In standard itoa    negative numbers are handled only with          base 10  Otherwise numbers are considered unsigned       if  num  lt  0  amp  amp  base    10                  isNegative   true           num   -num                    Process individual digits      while  num    0                  int rem   num   base           str i       rem  gt  9    rem-10     a    rem    0            num   num base                    If number is negative  append  -       if  isNegative           str i       -           str i      0      Append string terminator            Reverse the string      reverse str           return str       Another complete itoa   implementatiton  Reference Link An itoa   usage example below  Reference Link    include  lt stdio h gt   include  lt stdlib h gt   include  lt string h gt    int main         int a 54325      char buffer 20       itoa a buffer 2        here 2 means binary     printf  quot Binary value    s n quot   buffer         itoa a buffer 10        here 10 means decimal     printf  quot Decimal value    s n quot   buffer         itoa a buffer 16        here 16 means Hexadecimal     printf  quot Hexadecimal value    s n quot   buffer       return 0

[c] Converting int to string in C

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