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malloc.3: Document the reallocarray() added in glibc 2.26 

Signed-off-by: Michael Kerrisk <mtk.manpages@gmail.com>
This commit is contained in:
Michael Kerrisk 2017-06-19 16:27:58 +02:00
parent 4b80e269ee
commit 081eeee527
1 changed files with 53 additions and 1 deletions
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54
man3/malloc.3
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@ -41,7 +41,21 @@ malloc, free, calloc, realloc \- allocate and free dynamic memory
.BI "void free(void " "*ptr" );
.BI "void *calloc(size_t " "nmemb" ", size_t " "size" );
.BI "void *realloc(void " "*ptr" ", size_t " "size" );
.BI "void *reallocarray(void " "*ptr" ", size_t " nmemb ", size_t " "size" );
.fi
.PP
.in -4n
Feature Test Macro Requirements for glibc (see
.BR feature_test_macros (7)):
.in
.PP
.BR reallocarray ():
.br
.RS 4
.ad l
_GNU_SOURCE
.RE
.ad
.SH DESCRIPTION
.PP
The
@ -129,6 +143,34 @@ or
If the area pointed to was moved, a
.I free(ptr)
is done.
.PP
The
.BR reallocarray ()
function changes the size of the memory block pointed to by
.I ptr
to be large enough for an array of
.I nmemb
elements, each of which is
.I size
bytes.
It is equivalent to the call
.PP
.in +4n
realloc(ptr, nmemb * size);
.in
.PP
However, unlike that
.BR realloc ()
call,
.BR reallocarray ()
fails safely in the case where the multiplication would overflow.
If such an overflow occurs,
.BR reallocarray ()
returns NULL, sets
.I errno
to
.BR ENOMEM ,
and leaves the original block of memory unchanged.
.SH RETURN VALUE
The
.BR malloc ()
@ -168,11 +210,18 @@ is returned.
If
.BR realloc ()
fails, the original block is left untouched; it is not freed or moved.
.PP
On success, the
.BR reallocarray ()
function returns a pointer to the newly allocated memory.
On failure,
it returns NULL and the original block of memory is left untouched.
.SH ERRORS
.BR calloc (),
.BR malloc (),
.BR realloc (),
and
.BR realloc ()
.BR reallocarray ()
can fail with the following error:
.TP
.B ENOMEM
@ -205,6 +254,9 @@ T} Thread safety MT-Safe
.BR calloc (),
.BR realloc ():
POSIX.1-2001, POSIX.1-2008, C89, C99.
.PP
.BR reallocarray ()
is a nonstandard extension that first appeared in OpenBSD 5.6 and FreeBSD 11.0.
.SH NOTES
By default, Linux follows an optimistic memory allocation strategy.
This means that when