.\" 2007-06-15, Marc Boyer <marc.boyer@enseeiht.fr> + mtk
.\" Improve discussion of strncpy().
.\"
-.TH STRCPY 3 2015-03-02 "GNU" "Linux Programmer's Manual"
+.TH STRCPY 3 2019-03-06 "GNU" "Linux Programmer's Manual"
.SH NAME
strcpy, strncpy \- copy a string
.SH SYNOPSIS
.nf
.B #include <string.h>
-.sp
+.PP
.BI "char *strcpy(char *" dest ", const char *" src );
-.sp
+.PP
.BI "char *strncpy(char *" dest ", const char *" src ", size_t " n );
.fi
.SH DESCRIPTION
.BR strcpy ()
function copies the string pointed to by
.IR src ,
-including the terminating null byte (\(aq\\0\(aq),
+including the terminating null byte (\(aq\e0\(aq),
to the buffer pointed to by
.IR dest .
The strings may not overlap, and the destination string
A simple implementation of
.BR strncpy ()
might be:
+.PP
.in +4n
-.nf
-
+.EX
char *
strncpy(char *dest, const char *src, size_t n)
{
size_t i;
- for (i = 0; i < n && src[i] != \(aq\\0\(aq; i++)
+ for (i = 0; i < n && src[i] != \(aq\e0\(aq; i++)
dest[i] = src[i];
for ( ; i < n; i++)
- dest[i] = \(aq\\0\(aq;
+ dest[i] = \(aq\e0\(aq;
return dest;
}
-.fi
+.EE
.in
.SH RETURN VALUE
The
T} Thread safety MT-Safe
.TE
.SH CONFORMING TO
-SVr4, 4.3BSD, C89, C99.
+POSIX.1-2001, POSIX.1-2008, C89, C99, SVr4, 4.3BSD.
.SH NOTES
Some programmers consider
.BR strncpy ()
then
.BR strcpy ()
can be used.
-
+.PP
One valid (and intended) use of
.BR strncpy ()
is to copy a C string to a fixed-length buffer
while ensuring both that the buffer is not overflowed
-and that unused bytes in the target buffer are zeroed out
+and that unused bytes in the destination buffer are zeroed out
(perhaps to prevent information leaks if the buffer is to be
written to media or transmitted to another process via an
interprocess communication technique).
-
+.PP
If there is no terminating null byte in the first
.I n
bytes of
has length
.IR buflen ,
you can force termination using something like the following:
+.PP
.in +4n
-.nf
-
-strncpy(buf, str, buflen \- 1);
-if (buflen > 0)
- buf[buflen \- 1]= \(aq\\0\(aq;
-.fi
+.EX
+if (buflen > 0) {
+ strncpy(buf, str, buflen \- 1);
+ buf[buflen \- 1]= \(aq\e0\(aq;
+}
+.EE
.in
.PP
(Of course, the above technique ignores the fact that, if
.\"
.SS strlcpy()
Some systems (the BSDs, Solaris, and others) provide the following function:
-
+.PP
size_t strlcpy(char *dest, const char *src, size_t size);
-
+.PP
.\" http://static.usenix.org/event/usenix99/full_papers/millert/millert_html/index.html
.\" "strlcpy and strlcat - consistent, safe, string copy and concatenation"
.\" 1999 USENIX Annual Technical Conference
bytes to
.IR dest ,
always adds a terminating null byte,
-and does not pad the target with (further) null bytes.
+and does not pad the destination with (further) null bytes.
This function fixes some of the problems of
.BR strcpy ()
and