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,
   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

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

   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
   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.


   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>

   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)


   This  page  is  part of release 4.09 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


Personal Opportunity - Free software gives you access to billions of dollars of software at no cost. Use this software for your business, personal use or to develop a profitable skill. Access to source code provides access to a level of capabilities/information that companies protect though copyrights. Open source is a core component of the Internet and it is available to you. Leverage the billions of dollars in resources and capabilities to build a career, establish a business or change the world. The potential is endless for those who understand the opportunity.

Business Opportunity - Goldman Sachs, IBM and countless large corporations are leveraging open source to reduce costs, develop products and increase their bottom lines. Learn what these companies know about open source and how open source can give you the advantage.

Free Software

Free Software provides computer programs and capabilities at no cost but more importantly, it provides the freedom to run, edit, contribute to, and share the software. The importance of free software is a matter of access, not price. Software at no cost is a benefit but ownership rights to the software and source code is far more significant.

Free Office Software - The Libre Office suite provides top desktop productivity tools for free. This includes, a word processor, spreadsheet, presentation engine, drawing and flowcharting, database and math applications. Libre Office is available for Linux or Windows.

Free Books

The Free Books Library is a collection of thousands of the most popular public domain books in an online readable format. The collection includes great classical literature and more recent works where the U.S. copyright has expired. These books are yours to read and use without restrictions.

Source Code - Want to change a program or know how it works? Open Source provides the source code for its programs so that anyone can use, modify or learn how to write those programs themselves. Visit the GNU source code repositories to download the source.


Study at Harvard, Stanford or MIT - Open edX provides free online courses from Harvard, MIT, Columbia, UC Berkeley and other top Universities. Hundreds of courses for almost all major subjects and course levels. Open edx also offers some paid courses and selected certifications.

Linux Manual Pages - A man or manual page is a form of software documentation found on Linux/Unix operating systems. Topics covered include computer programs (including library and system calls), formal standards and conventions, and even abstract concepts.