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STRCAT(3)		   Linux Programmer's Manual		     STRCAT(3)

       strcat, strncat - concatenate two strings

       #include <string.h>

       char *strcat(char *dest, const char *src);

       char *strncat(char *dest, const char *src, size_t n);

       The  strcat() function appends the src string to the dest string, over-
       writing the terminating null byte ('\0') at the end of dest,  and  then
       adds  a	terminating  null  byte.  The strings may not overlap, and the
       dest string must have enough space for the  result.   If	 dest  is  not
       large  enough, program behavior is unpredictable; buffer overruns are a
       favorite avenue for attacking secure programs.

       The strncat() function is similar, except that

       *  it will use at most n bytes from src; and

       *  src does not need to be null-terminated if it	 contains  n  or  more

       As  with	 strcat(),  the resulting string in dest is always null-termi-

       If src contains n or more bytes, strncat() writes n+1 bytes to dest  (n
       from  src plus the terminating null byte).  Therefore, the size of dest
       must be at least strlen(dest)+n+1.

       A simple implementation of strncat() might be:

	   char *
	   strncat(char *dest, const char *src, size_t n)
	       size_t dest_len = strlen(dest);
	       size_t i;

	       for (i = 0 ; i < n && src[i] != '\0' ; i++)
		   dest[dest_len + i] = src[i];
	       dest[dest_len + i] = '\0';

	       return dest;

       The strcat() and strncat() functions return a pointer to the  resulting
       string dest.

       For   an	  explanation	of   the  terms	 used  in  this	 section,  see

       |Interface	    | Attribute	    | Value   |
       |strcat(), strncat() | Thread safety | MT-Safe |
       POSIX.1-2001, POSIX.1-2008, C89, C99, SVr4, 4.3BSD.

       Some systems (the BSDs, Solaris,	 and  others)  provide	the  following

	   size_t strlcat(char *dest, const char *src, size_t size);

       This  function  appends	the  null-terminated  string src to the string
       dest, copying at most size-strlen(dest)-1 from src, and adds  a	termi-
       nating  null byte to the result, unless size is less than strlen(dest).
       This function fixes the buffer overrun problem  of  strcat(),  but  the
       caller  must  still  handle the possibility of data loss if size is too
       small.  The function returns the length of the string  strlcat()	 tried
       to  create;  if the return value is greater than or equal to size, data
       loss occurred.  If data loss matters, the caller must either check  the
       arguments  before  the  call, or test the function return value.	 strl-
       cat() is not present in glibc and is not standardized by POSIX, but  is
       available on Linux via the libbsd library.

       Because	strcat() and strncat() must find the null byte that terminates
       the string dest using a search that starts  at  the  beginning  of  the
       string,	the  execution time of these functions scales according to the
       length of the string dest.  This can be	demonstrated  by  running  the
       program below.  (If the goal is to concatenate many strings to one tar-
       get, then manually copying the bytes  from  each	 source	 string	 while
       maintaining a pointer to the end of the target string will provide bet-
       ter performance.)

   Program source

       #include <string.h>
       #include <time.h>
       #include <stdio.h>

       main(int argc, char *argv[])
       #define LIM 4000000
	   int j;
	   char p[LIM];
	   time_t base;

	   base = time(NULL);
	   p[0] = '\0';

	   for (j = 0; j < LIM; j++) {
	       if ((j % 10000) == 0)
		   printf("%d %ld\n", j, (long) (time(NULL) - base));
	       strcat(p, "a");

       bcopy(3),  memccpy(3),  memcpy(3),  strcpy(3),  string(3),  strncpy(3),
       wcscat(3), wcsncat(3)

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       description of the project, information about reporting bugs,  and  the
       latest	  version     of     this    page,    can    be	   found    at

GNU				  2016-07-17			     STRCAT(3)