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
       ('\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 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] != '\0' ; i++)
                   dest[dest_len + i] = src[i];
               dest[dest_len + i] = '\0';

               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 terminating 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 + 1];    /* +1 for terminating null byte */
           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");
           }
       }

SEE ALSO

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

COLOPHON

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