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 terminat‐
       ing 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
   Multithreading (see pthreads(7))
       The strcat() and strncat() functions are thread-safe.

CONFORMING TO
       SVr4, 4.3BSD, C89, C99.

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.  strl‐
       cat()  is not present in glibc and is not standardized by POSIX, but is available on Linux
       via the libbsd library.

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 3.74 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 http://www.kernel.org/doc/man-pages/.



GNU                                         2014-01-20                                  STRCAT(3)