strftime.3: Clarify details of return value

Signed-off-by: Michael Kerrisk <mtk.manpages@gmail.com>

man3/strftime.3

@@ -34,7 +34,7 @@
 .\" 2005-11-22 mtk, added Glibc Notes covering optional 'flag' and
 .\"           'width' components of conversion specifications.
 .\"
-.TH STRFTIME 3  2012-05-10 "GNU" "Linux Programmer's Manual"
+.TH STRFTIME 3  2013-06-28 "GNU" "Linux Programmer's Manual"
 .SH NAME
 strftime \- format date and time
 .SH SYNOPSIS
@@ -325,24 +325,33 @@ is defined in
 See also
 .BR ctime (3).
 .SH RETURN VALUE
-The
+Provided that the result string,
+including the terminating null byte, does not exceed
+.I max
+bytes,
 .BR strftime ()
-function returns the number of bytes placed
-in the array
-.IR s ,
-not including the terminating null byte,
-provided the string, including the terminating null byte, fits.
-Otherwise, it returns 0, and the contents of the array are undefined.
+returns the number of bytes (excluding the terminating null byte)
+placed in the array
+.IR s .
+If the length of the result string (including the terminating null byte)
+would exceed
+.I max
+bytes, then
+.BR strftime ()
+returns 0, and the contents of the array are undefined.
 (This behavior applies since at least libc 4.4.4;
 very old versions of libc, such as libc 4.4.1,
 would return
 .I max
 if the array was too small.)
 .LP
-Note that the return value 0 does not necessarily indicate an error;
-for example, in many locales
+Note that the return value 0 does not necessarily indicate an error.
+For example, in many locales
 .B %p
 yields an empty string.
+An empty 
+.I format
+string will likewise yield an empty string.
 .SH ENVIRONMENT
 The environment variables
 .B TZ