[review] manual: Clarify strnlen, wcsnlen, strndup null termination behavior

["Florian Weimer (Code Review)" <gerrit at gnutoolchain-gerrit dot osci dot io>]

Change URL: https://gnutoolchain-gerrit.osci.io/r/c/glibc/+/444
......................................................................

manual: Clarify strnlen, wcsnlen, strndup null termination behavior

It is required that the inputs are arrays, as reading is not
guaranteed to stop on the first null byte.

Change-Id: Ia3e68bc2d4d7e967df141702fb2f600cbd4a6432
---
M manual/string.texi
1 file changed, 10 insertions(+), 0 deletions(-)



diff --git a/manual/string.texi b/manual/string.texi
index a1c58e5..ba8a588 100644
--- a/manual/string.texi
+++ b/manual/string.texi
@@ -328,6 +328,10 @@
     @result{} 5
 @end smallexample
 
+Note that @var{s} must be an array of at least @var{maxlen} bytes.  It
+is undefined to call @code{strnlen} on a shorter array, even if it is
+known that the shorter array contains a null terminator.
+
 This function is a GNU extension and is declared in @file{string.h}.
 @end deftypefun
 
@@ -336,6 +340,8 @@
 @safety{@prelim{}@mtsafe{}@assafe{}@acsafe{}}
 @code{wcsnlen} is the wide character equivalent to @code{strnlen}.  The
 @var{maxlen} parameter specifies the maximum number of wide characters.
+Similar to @code{strnlen}, @var{ws} must point to an array of at least
+@var{maxlen} wide characters.
 
 This function is a GNU extension and is declared in @file{wchar.h}.
 @end deftypefun
@@ -919,6 +925,10 @@
 copies just the first @var{size} bytes and adds a closing null byte.
 Otherwise all bytes are copied and the string is terminated.
 
+Note that @var{s} must be an array of at least @var{size} bytes.  It
+is undefined to call @code{strndup} on a shorter array, even if it is
+known that the shorter array contains a null terminator.
+
 This function differs from @code{strncpy} in that it always terminates
 the destination string.
 

-- 
Gerrit-Project: glibc
Gerrit-Branch: master
Gerrit-Change-Id: Ia3e68bc2d4d7e967df141702fb2f600cbd4a6432
Gerrit-Change-Number: 444
Gerrit-PatchSet: 1
Gerrit-Owner: Florian Weimer <fweimer@redhat.com>
Gerrit-MessageType: newchange