Rick, On 03/01/2014 07:31 PM, Rick Stanley wrote: > On the current page for `man 3 strncpy` there is an error in the sample > for forced termination if the copy does not result in a proper > null-terminated string. (Appears in both "Man-pages, release 3.58", and > on http://man7.org/linux/man-pages/man3/strncpy.3.html ) > > Current: > > strncpy(buf, str, n); > if (n > 0) > buf[n - 1]= '\0'; > > If n == 4, then 4 bytes are copied, (buf[0] - buf[3]) but n - 1 or > buf[3] is then overwritten with the '\0'. Should be buf[n] instead. > > Corrected code: > > strncpy(buf, str, n); > if (n > 0) > buf[n]= '\0'; > > Question: Even if n == 0 why shouldn't buf[n] be set to '\0'? The answer to all the points is that there was a mistake in the first line of the code. It should have read: strncpy(buf, str, n - 1); As long as I was there, I decided to improve the text somewhat as well. Patch below. Thanks for the report. Cheers, Michael diff --git a/man3/strcpy.3 b/man3/strcpy.3 index da027c3..c4293b0 100644 --- a/man3/strcpy.3 +++ b/man3/strcpy.3 @@ -32,7 +32,7 @@ .\" 2007-06-15, Marc Boyer <marc.boyer@xxxxxxxxxxx> + mtk .\" Improve discussion of strncpy(). .\" -.TH STRCPY 3 2014-02-28 "GNU" "Linux Programmer's Manual" +.TH STRCPY 3 2014-03-04 "GNU" "Linux Programmer's Manual" .SH NAME strcpy, strncpy \- copy a string .SH SYNOPSIS @@ -152,20 +152,25 @@ bytes of .BR strncpy () produces an unterminated string in .IR dest . -You can force termination using something like the following: +If +.I buf +has length +.IR buflen , +you can force termination using something like the following: .in +4n .nf -strncpy(buf, str, n); -if (n > 0) - buf[n \- 1]= \(aq\\0\(aq; +strncpy(buf, str, buflen \- 1); +if (buflen > 0) + buf[buflen \- 1]= \(aq\\0\(aq; .fi .in .PP -(Of course, the above technique ignores the fact that -information contained in +(Of course, the above technique ignores the fact that, if .I src -is lost in the copying to +contains more than +.I "buflen\ \-\ 1" +bytes, information is lost in the copying to .IR dest .) Some systems (the BSDs, Solaris, and others) provide the following function: -- Michael Kerrisk Linux man-pages maintainer; http://www.kernel.org/doc/man-pages/ Linux/UNIX System Programming Training: http://man7.org/training/ -- To unsubscribe from this list: send the line "unsubscribe linux-man" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
