NAME
strncpy —
copy part of a string to
another
SYNOPSIS
#include
<string.h>
char *
strncpy(char
*dst, const char
*src, size_t
len);
DESCRIPTION
The
strncpy()
function copies not more than len characters from the
string src to the buffer dst. If
src is less than len characters
long, it fills the remaining buffer with
‘\0’ characters. If the length of
src is greater than or equal to
len, dst will
not be
NUL-terminated.
strncpy()
only NUL
terminates the destination string when the length of the source string is
less than the length parameter.
If the src and dst strings overlap, the behavior is undefined.
RETURN VALUES
The strncpy() function returns
dst.
EXAMPLES
The following sets chararray to “abc\0\0\0”:
(void)strncpy(chararray, "abc", 6);
The following sets chararray to “abcdef”, without a NUL-terminator:
(void)strncpy(chararray, "abcdefgh", 6);
The following sequence copies as many characters from input to buf as will fit, and then NUL terminates the result by hand:
char buf[BUFSIZ]; (void)strncpy(buf, input, sizeof(buf) - 1); buf[sizeof(buf) - 1] = '\0';
By now it is clear that strncpy is
dangerously easy to misuse. The
strlcpy(3) function is safer for this kind of operation:
if (strlcpy(buf, input, sizeof(buf)) >= sizeof(buf))
goto toolong;
SEE ALSO
STANDARDS
The strncpy() function conforms to
ANSI X3.159-1989
(“ANSI C89”).
HISTORY
The strncpy() function first appeared in
Version 7 AT&T UNIX.