STRCPY man page on Archlinux

Man page or keyword search:  
man Server   11224 pages
apropos Keyword Search (all sections)
Output format
Archlinux logo
[printable version]

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

       strcpy, strncpy - copy a string

       #include <string.h>

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

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

       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.  Beware  of  buffer  overruns!	  (See

       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() writes additional null
       bytes to dest to ensure that a total of n bytes are written.

       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;

       The strcpy() and strncpy() functions return a pointer to	 the  destina‐
       tion string dest.

   Multithreading (see pthreads(7))
       The strcpy() and strncpy() functions are thread-safe.

       SVr4, 4.3BSD, C89, C99.

       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.

       One  valid  (and	 intended) use of strncpy() is to copy a C string to a
       fixed-length buffer while ensuring both that the buffer	is  not	 over‐
       flowed  and that unused bytes in the target buffer are zeroed out (per‐
       haps to prevent information leaks if the buffer is  to  be  written  to
       media  or transmitted to another process via an interprocess communica‐
       tion technique).

       If there is no terminating null byte in	the  first  n  bytes  of  src,
       strncpy()  produces  an unterminated string in dest.  If buf has length
       buflen, you can force termination using something like the following:

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

       (Of course, the above technique ignores the fact that, if src  contains
       more  than  buflen - 1  bytes,  information  is	lost in the copying to

       Some systems (the BSDs, Solaris,	 and  others)  provide	the  following

	   size_t strlcpy(char *dest, const char *src, size_t size);

       This  function  is  similar  to strncpy(), but it copies at most size-1
       bytes to dest, always adds a terminating null byte, and	does  not  pad
       the  target with (further) null bytes.  This function fixes some of the
       problems of strcpy() and strncpy(), but the caller  must	 still	handle
       the possibility of data loss if size is too small.  The return value of
       the function is the length of src, which allows truncation to be easily
       detected: if the return value is greater than or equal to size, trunca‐
       tion occurred.  If loss of data matters, the caller must	 either	 check
       the  arguments  before  the  call,  or  test the function return value.
       strlcpy() is not present in glibc and is not standardized by POSIX, but
       is available on Linux via the libbsd library.

       If  the destination string of a strcpy() is not large enough, then any‐
       thing 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 unneces‐
       sary if you can show that overflow is impossible, but be careful:  pro‐
       grams  can  get changed over time, in ways that may make the impossible

       bcopy(3), memccpy(3),  memcpy(3),  memmove(3),  stpcpy(3),  stpncpy(3),
       strdup(3), string(3), wcscpy(3), wcsncpy(3)

       This  page  is  part of release 3.65 of the Linux man-pages project.  A
       description of the project, and information about reporting  bugs,  can
       be found at

GNU				  2014-03-04			     STRCPY(3)

List of man pages available for Archlinux

Copyright (c) for man pages and the logo by the respective OS vendor.

For those who want to learn more, the polarhome community provides shell access and support.

[legal] [privacy] [GNU] [policy] [cookies] [netiquette] [sponsors] [FAQ]
Polarhome, production since 1999.
Member of Polarhome portal.
Based on Fawad Halim's script.
Vote for polarhome
Free Shell Accounts :: the biggest list on the net