man3/malloc_usable_size.3

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  25 .TH MALLOC_USABLE_SIZE 3  2017-09-15 "GNU" "Linux Programmer's Manual"
  26 .SH NAME
  27 malloc_usable_size \- obtain size of block of memory allocated from heap
  28 .SH SYNOPSIS
  29 .B #include <malloc.h>
  30 .PP
  31 .BI "size_t malloc_usable_size (void *" ptr );
  32 .SH DESCRIPTION
  33 The
  34 .BR malloc_usable_size ()
  35 function returns the number of usable bytes in the block pointed to by
  36 .IR ptr ,
  37 a pointer to a block of memory allocated by
  38 .BR malloc (3)
  39 or a related function.
  40 .SH RETURN VALUE
  41 .BR malloc_usable_size ()
  42 returns the number of usable bytes in
  43 the block of allocated memory pointed to by
  44 .IR ptr .
  45 If
  46 .I ptr
  47 is NULL, 0 is returned.
  48 .SH ATTRIBUTES
  49 For an explanation of the terms used in this section, see
  50 .BR attributes (7).
  51 .TS
  52 allbox;
  53 lbw20 lb lb
  54 l l l.
  55 Interface       Attribute       Value
  56 T{
  57 .BR malloc_usable_size ()
  58 T}      Thread safety   MT-Safe
  59 .TE
  60 .SH CONFORMING TO
  61 This function is a GNU extension.
  62 .SH NOTES
  63 The value returned by
  64 .BR malloc_usable_size ()
  65 may be greater than the requested size of the allocation because
  66 of alignment and minimum size constraints.
  67 Although the excess bytes can be overwritten by the application
  68 without ill effects,
  69 this is not good programming practice:
  70 the number of excess bytes in an allocation depends on
  71 the underlying implementation.
  72 .PP
  73 The main use of this function is for debugging and introspection.
  74 .SH SEE ALSO
  75 .BR malloc (3)