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),  stpncpy(3),  strdup(3),
       string(3), wcscpy(3), wcsncpy(3)

COLOPHON
       This page is part of release 3.35 of the Linux man-pages project.   A  description  of
       the   project,   and   information   about   reporting   bugs,   can   be   found   at
       http://man7.org/linux/man-pages/.



GNU                                       2010-09-20                                STRCPY(3)