MALLOC_USABLE_SIZE(3) Linux Programmer's Manual MALLOC_USABLE_SIZE(3)
NAME
malloc_usable_size - obtain size of block of memory allocated from heap
SYNOPSIS
#include <malloc.h>
size_t malloc_usable_size (void *ptr);
DESCRIPTION
The malloc_usable_size() function returns the number of usable bytes in
the block pointed to by ptr, a pointer to a block of memory allocated
by malloc(3) or a related function.
RETURN VALUE
malloc_usable_size() returns the number of usable bytes in the block of
allocated memory pointed to by ptr. If ptr is NULL, 0 is returned.
ATTRIBUTES
For an explanation of the terms used in this section, see at-
tributes(7).
+---------------------+---------------+---------+
|Interface | Attribute | Value |
+---------------------+---------------+---------+
|malloc_usable_size() | Thread safety | MT-Safe |
+---------------------+---------------+---------+
CONFORMING TO
This function is a GNU extension.
NOTES
The value returned by malloc_usable_size() may be greater than the re-
quested size of the allocation because of alignment and minimum size
constraints. Although the excess bytes can be overwritten by the ap-
plication without ill effects, this is not good programming practice:
the number of excess bytes in an allocation depends on the underlying
implementation.
The main use of this function is for debugging and introspection.
SEE ALSO
malloc(3)
COLOPHON
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latest version of this page, can be found at
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GNU 2017-09-15 MALLOC_USABLE_SIZE(3)