malloc_usable_size(3)	    Library Functions Manual	   malloc_usable_size(3)

NAME
     malloc_usable_size - obtain size of block of memory allocated from heap

LIBRARY
     Standard C library (libc, -lc)

SYNOPSIS
     #include <malloc.h>

     size_t malloc_usable_size(void *_Nullable ptr);

DESCRIPTION
     This  function  can be used for diagnostics or statistics about allocations
     from malloc(3) or a related function.

RETURN VALUE
     malloc_usable_size() returns a value no less than the size of 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 attributes(7).
     allbox; lbx lb lb l l l.  Interface Attribute Value T{ malloc_usable_size()
     T}	  Thread safety	  MT-Safe

STANDARDS
     GNU.

CAVEATS
     The value returned by malloc_usable_size() may  be	 greater  than	the  re-
     quested  size  of the allocation because of various internal implementation
     details, none of which the programmer should rely on.  This function is in-
     tended to only be used for diagnostics and statistics; writing to	the  ex-
     cess  memory  without  first calling realloc(3) to resize the allocation is
     not supported.  The returned value is only valid at the time of the call.

SEE ALSO
     malloc(3)

Linux man-pages 6.18		   2026-02-08		   malloc_usable_size(3)