strncpy(3) - NetBSD Manual Pages

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STRCPY(3)               NetBSD Library Functions Manual              STRCPY(3)


NAME

     stpcpy, stpncpy, strcpy, strncpy -- copy strings


LIBRARY

     Standard C Library (libc, -lc)


SYNOPSIS

     #include <string.h>

     char *
     stpcpy(char * restrict dst, const char * restrict src);

     char *
     stpncpy(char * restrict dst, const char * restrict src, size_t len);

     char *
     strcpy(char * restrict dst, const char * restrict src);

     char *
     strncpy(char * restrict dst, const char * restrict src, size_t len);


DESCRIPTION

     The stpcpy() and strcpy() functions copy the string src to dst (including
     the terminating `\0' character).

     The stpncpy() and strncpy() functions copy at most len characters from
     src into dst.  If src is less than len characters long, the remainder of
     dst is filled with `\0' characters.  Otherwise, dst is not terminated.


RETURN VALUES

     The strcpy() and strncpy() functions return dst.  The stpcpy() and
     stpncpy() functions return a pointer to the terminating `\0' character of
     dst.  If stpncpy() does not terminate dst with a NUL character, it
     instead returns a pointer to dst[len] (which does not necessarily refer
     to a valid memory location.)


EXAMPLES

     The following sets chararray to ``abc\0\0\0'':

           char chararray[6];

           (void)strncpy(chararray, "abc", sizeof(chararray));

     The following sets chararray to ``abcdef'':

           char chararray[6];

           (void)strncpy(chararray, "abcdefgh", sizeof(chararray));

     Note that it does not NUL-terminate chararray because the length of the
     source string is greater than or equal to the length parameter.
     strncpy() only NUL-terminates the destination string when the length of
     the source string is less than the length parameter.

     The following copies as many characters from input to buf as will fit and
     NUL-terminates the result.  Because strncpy() does not guarantee to
     NUL-terminate the string itself, this must be done explicitly.

           char buf[1024];

           (void)strncpy(buf, input, sizeof(buf) - 1);
           buf[sizeof(buf) - 1] = '\0';

     This could be better and more simply achieved using strlcpy(3), as shown
     in the following example:

           (void)strlcpy(buf, input, sizeof(buf));

     Note that because strlcpy(3) is not defined in any standards, it should
     only be used when portability is not a concern.


SEE ALSO

     bcopy(3), memccpy(3), memcpy(3), memmove(3), strlcpy(3), wcscpy(3)


STANDARDS

     The strcpy() and strncpy() functions conform to ISO/IEC 9899:1999
     (``ISO C99'').  The stpcpy() and stpncpy() functions conform to IEEE Std
     1003.1-2008 (``POSIX.1'').


HISTORY

     The stpcpy() and stpncpy() functions first appeared in NetBSD 6.0.


SECURITY CONSIDERATIONS

     The strcpy() and stpcpy() functions are easily misused in a manner which
     enables malicious users to arbitrarily change a running program's func-
     tionality through a buffer overflow attack.

NetBSD 7.1.2                      May 1, 2009                     NetBSD 7.1.2