STRCPY(3) BSD 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 *dst, const char *src);
char *
stpncpy(char *restrict dst, const char *restrict src, size_t n);
char *
strcpy(char *restrict dst, const char *restrict src);
char *
strncpy(char *restrict dst, const char *restrict src, size_t n);
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 n characters from src
into dst. If src is less than n characters long, the remainder of dst is
filled with ‘\0’ characters. Otherwise, dst is not terminated.
The source and destination strings should not overlap, as the behavior is
undefined.
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[n] (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 argument.
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 achieved using strlcpy(3), as shown in the following
example:
(void)strlcpy(buf, input, sizeof(buf));
SECURITY CONSIDERATIONS
The strcpy(), strncpy(), stpcpy(), and stpncpy() functions are easily
misused in a manner which enables malicious users to arbitrarily change a
running program's functionality through a buffer overflow attack. (See
the FSA and EXAMPLES.)
It is recommended that strlcpy(3) be used instead as a way to avoid such
problems. strlcpy(3) is not defined in any standards, but it has been
adopted by most major libc implementations.
SEE ALSObcopy(3), memccpy(3), memcpy(3), memmove(3), strlcpy(3), wcscpy(3)STANDARDS
The strcpy() and strncpy() functions conform to ISO/IEC 9899:1990
(“ISO C90”). The stpcpy() and stpncpy() functions conform to IEEE Std
1003.1-2008 (“POSIX.1”).
HISTORY
The stpcpy() function first appeared in FreeBSD 4.4, and stpncpy() was
added in FreeBSD 8.0.
BSD February 28, 2009 BSD
