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

NAME

       strcat, strncat - concatenate two strings

SYNOPSIS

       #include <string.h>

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

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

DESCRIPTION

       The  strcat() function appends the src string to the dest string, overwriting the terminating null byte ('') 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 bytes.

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

       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] != '' ; i++)
		   dest[dest_len + i] = src[i];
	       dest[dest_len + i] = '';

	       return dest;
	   }

RETURN VALUE

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

ATTRIBUTES

       For an explanation of the terms used in this section, see attributes(7).

       +--------------------+---------------+---------+
       |Interface	    | Attribute     | Value   |
       +--------------------+---------------+---------+
       |strcat(), strncat() | Thread safety | MT-Safe |
       +--------------------+---------------+---------+
CONFORMING TO

       POSIX.1-2001, POSIX.1-2008, C89, C99, SVr4, 4.3BSD.

NOTES

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

	   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 terminat-
       ing  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.  strlcat() is not present in glibc and is not standardized by POSIX,  but
       is available on Linux via the libbsd library.

EXAMPLE

       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 target, then manually copying the bytes from each source string while
       maintaining a pointer to the end of the target string will provide better performance.)

   Program source

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

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

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

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

SEE ALSO

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

COLOPHON

       This page is part of release 4.15 of the Linux man-pages project.  A description of the project, information about reporting bugs, and  the
       latest version of this page, can be found at https://www.kernel.org/doc/man-pages/.

GNU
								    2017-09-15								 STRCAT(3)