A more detailed notice is on realloc(3p).
......
$ man 3p realloc \
|sed -n \
-e '/APPLICATION USAGE/,/^$/p' \
-e '/FUTURE DIRECTIONS/,/^$/p';
APPLICATION USAGE
The description of realloc() has been modified from pre‐
vious versions of this standard to align with the
ISO/IEC 9899:1999 standard. Previous versions explicitly
permitted a call to realloc(p, 0) to free the space
pointed to by p and return a null pointer. While this be‐
havior could be interpreted as permitted by this version
of the standard, the C language committee have indicated
that this interpretation is incorrect. Applications
should assume that if realloc() returns a null pointer,
the space pointed to by p has not been freed. Since this
could lead to double-frees, implementations should also
set errno if a null pointer actually indicates a failure,
and applications should only free the space if errno was
changed.
FUTURE DIRECTIONS
This standard defers to the ISO C standard. While that
standard currently has language that might permit real‐
loc(p, 0), where p is not a null pointer, to free p while
still returning a null pointer, the committee responsible
for that standard is considering clarifying the language
to explicitly prohibit that alternative.
Bug: 211039 <https://bugzilla.kernel.org/show_bug.cgi?id=211039>
Reported-by: Johannes Pfister <johannes.pfister@xxxxxxxxxxx>
Cc: libc-alpha@xxxxxxxxxxxxxx
Signed-off-by: Alejandro Colomar <alx.manpages@xxxxxxxxx>
---
Hi Johannes, Michael,
Thanks for the report, Johannes!
Please review that your name is correct (I guessed it from the email).
Michael, please review the wording.
Thanks,
Alex
man3/malloc.3 | 18 +++++++++++++++++-
1 file changed, 17 insertions(+), 1 deletion(-)
diff --git a/man3/malloc.3 b/man3/malloc.3
index d8b4da62f..467e2438a 100644
--- a/man3/malloc.3
+++ b/man3/malloc.3
@@ -149,7 +149,8 @@ is equal to zero,
and
.I ptr
is not NULL, then the call is equivalent to
-.IR free(ptr) .
+.I free(ptr)
+(this behavior is nonportable; see NOTES).
Unless
.I ptr
is NULL, it must have been returned by an earlier call to
@@ -375,6 +376,21 @@ The
implementation is tunable via environment variables; see
.BR mallopt (3)
for details.
+.SS Nonportable behavior
+The behavior of
+.BR realloc ()
+when
+.I size
+is equal to zero,
+and
+.I ptr
+is not NULL,
+is glibc specific;
+other implementations may return NULL, and set
+.IR errno .
+Portable POSIX programs should avoid it.
+See
+.BR realloc (3p).
.SH SEE ALSO
.\" http://g.oswego.edu/dl/html/malloc.html
.\" A Memory Allocator - by Doug Lea
--
2.30.0
