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



NAME
       strcpy, strncpy - copy a string

SYNOPSIS
       #include <string.h>

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

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

DESCRIPTION
       The  strcpy()  function  copies  the  string pointed to by src, including the terminating null byte ('\0'), to the buffer
       pointed to by dest.  The strings may not overlap, and the destination string dest must be large  enough  to  receive  the
       copy.

       The  strncpy()  function  is  similar,  except that at most n bytes of src are copied.  Warning: If there is no null byte
       among the first n bytes of src, the string placed in dest will not be null-terminated.

       If the length of src is less than n, strncpy() pads the remainder of dest with null bytes.

       A simple implementation of strncpy() might be:

           char*
           strncpy(char *dest, const char *src, size_t n){
               size_t i;

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

               return dest;
           }

RETURN VALUE
       The strcpy() and strncpy() functions return a pointer to the destination string dest.

CONFORMING TO
       SVr4, 4.3BSD, C89, C99.

NOTES
       Some programmers consider strncpy() to be inefficient and error prone.  If the programmer knows (i.e., includes  code  to
       test!)  that the size of dest is greater than the length of src, then strcpy() can be used.

       If there is no terminating null byte in the first n characters of src, strncpy() produces an unterminated string in dest.
       Programmers often prevent this mistake by forcing termination as follows:

           strncpy(buf, str, n);
           if (n > 0)
               buf[n - 1]= '\0';

BUGS
       If the destination string of a strcpy() is not large enough, then anything might happen.  Overflowing fixed-length string
       buffers  is  a favorite cracker technique for taking complete control of the machine.  Any time a program reads or copies
       data into a buffer, the program first needs to check that there's enough space.  This may be unnecessary if you can  show
       that  overflow  is  impossible,  but be careful: programs can get changed over time, in ways that may make the impossible
       possible.

SEE ALSO
       bcopy(3), memccpy(3), memcpy(3), memmove(3), stpcpy(3), strdup(3), wcscpy(3), wcsncpy(3)

COLOPHON
       This page is part of release 3.25 of the Linux man-pages project.  A description of the project,  and  information  about
       reporting bugs, can be found at http://www.kernel.org/doc/man-pages/.



GNU                                                        2009-12-04                                                  STRCPY(3)