Append Char To String in C

Question

How do I append a single char to a string in C   i e   char  str    blablabla   char c    H   str append str c      blablablaH

User · Answer

To append a char to a string in C  you first have to ensure that the memory buffer containing the string is large enough to accomodate an extra character  In your example program  you d have to allocate a new  additional  memory block because the given literal string cannot be modified   Here s a sample    include  lt stdlib h gt   int main         char  str    blablabla       char c    H        size t len   strlen str       char  str2   malloc len   1   1       one for extra char  one for trailing zero        strcpy str2  str       str2 len    c      str2 len   1      0        printf    s n   str2       prints  blablablaH          free  str2        First  use malloc to allocate a new chunk of memory which is large enough to accomodate all characters of the input string  the extra char to append - and the final zero  Then call strcpy to copy the input string into the new buffer  Finally  change the last two bytes in the new buffer to tack on the character to add as well as the trailing zero

User · Answer

I do not think you can declare a string like that in c  You may only do that for const char  and of course you can not modify a const char   as it is const    You may use dynamic char array but you will have to take care of the reallocation   EDIT  in fact this syntax compiles correctly  Still you can should not modify what str points to if it is initialized in the way you do it  from string literal

User · Answer

here s it  it WORKS 100   char  appending char  cArr  const char c      int len   strlen cArr    cArr len   1    cArr len    cArr len    c   return cArr

User · Answer

In my case  this was the best solution I found   snprintf str  sizeof str    s c   str  c

User · Answer

You can use strncat    include  lt stdio h gt   include  lt string h gt   int main void     char hi 6     char ch          strcpy hi   quot hello quot       strncat hi   amp ch  1     printf  quot  s n quot   hi

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C does not have strings per se -- what you have is a char pointer pointing to some read-only memory containing the characters  blablabla 0   In order to append a character there  you need a  writable memory and b  enough space for the string in its new form  The string literal  blablabla 0  has neither   The solutions are   1  Use malloc   et al  to dynamically allocate memory   Don t forget to free   afterwards   2  Use a char array   When working with strings  consider using strn  variants of the str  functions -- they will help you stay within memory bounds

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The Original poster didn t mean to write      char  str    blablabla     but    char str 128     blablabla     Now  adding a single character would seem more efficient than adding a whole string with strcat   Going the strcat way  you could     char tmpstr 2     tmpstr 0    c    tmpstr 1    0    strcat  str  tmpstr     but you can also easily write your own function  as several have done before me      void strcat c  char  str  char c          for    str str        note the terminating semicolon here        str     c        str     0

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Create a new string  string   char    include  lt stdio h gt       include  lt stdlib h gt    define ERR MESSAGE  NO MEM  Not enough memory    define allocator element  type   allocator element  sizeof type        Allocator function  safe alloc     void   allocator size t element  size t typeSize        void  ptr   NULL         check alloc        if   ptr   calloc element  typeSize      NULL       printf ERR MESSAGE  NO MEM   exit 1           return pointer        return ptr         Append function  safe mode     char  append const char  input  const char c        char  newString   ptr          alloc        newString   allocator  strlen input    2   char          Copy old string in new  with pointer         ptr   newString      for    input  input      ptr    input  ptr            Copy char at end         ptr   c         return new string  for dealloc use free            return newString         Program main    int main  int argc  const char  argv          char  input    Ciao Mondo      i am italian     this is  Hello World      char c            char  newString       newString   append input  c       printf   s n  newString          dealloc        free newString       newString   NULL       exit 0                    0   1   2   3    4    5   6   7   8   9  10   11 newString is  C   i   a   o    32   M   o   n   d   o        0    Don t alter the array size   len  1   etc   without know its exact size  it may damage other data  alloc an array with the new size and put the old data inside instead  remember that  for a char array  the last value must be  0  calloc   sets all values to  0  which is excellent for char arrays   I hope this helps

User · Answer

char  str    blablabla          You should not modify this string at all  It resides in implementation defined read only region  Modifying it causes Undefined Behavior        You need a char array not a string literal        Good Read  What is the difference between char a      string   and char  p    string

User · Answer

If Linux is your concern  the easiest way to append two strings  char   append char   string1  char   string2        char   result   NULL      asprintf  amp result   quot  s s quot   string1  string2       return result     This won t work with MS Visual C  Note  you have to free   the memory returned by asprintf

[c] Append Char To String in C?

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