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| .TH MALLOC_USABLE_SIZE 3 2021-03-22 "GNU" "Linux Programmer's Manual" |
| .SH NAME |
| malloc_usable_size \- obtain size of block of memory allocated from heap |
| .SH SYNOPSIS |
| .nf |
| .B #include <malloc.h> |
| .PP |
| .BI "size_t malloc_usable_size (void *" ptr ); |
| .fi |
| .SH DESCRIPTION |
| The |
| .BR malloc_usable_size () |
| function returns the number of usable bytes in the block pointed to by |
| .IR ptr , |
| a pointer to a block of memory allocated by |
| .BR malloc (3) |
| or a related function. |
| .SH RETURN VALUE |
| .BR malloc_usable_size () |
| returns the number of usable bytes in |
| the block of allocated memory pointed to by |
| .IR ptr . |
| If |
| .I ptr |
| is NULL, 0 is returned. |
| .SH ATTRIBUTES |
| For an explanation of the terms used in this section, see |
| .BR attributes (7). |
| .ad l |
| .nh |
| .TS |
| allbox; |
| lbx lb lb |
| l l l. |
| Interface Attribute Value |
| T{ |
| .BR malloc_usable_size () |
| T} Thread safety MT-Safe |
| .TE |
| .hy |
| .ad |
| .sp 1 |
| .SH CONFORMING TO |
| This function is a GNU extension. |
| .SH NOTES |
| The value returned by |
| .BR malloc_usable_size () |
| may be greater than the requested size of the allocation because |
| of alignment and minimum size constraints. |
| Although the excess bytes can be overwritten by the application |
| without ill effects, |
| this is not good programming practice: |
| the number of excess bytes in an allocation depends on |
| the underlying implementation. |
| .PP |
| The main use of this function is for debugging and introspection. |
| .SH SEE ALSO |
| .BR malloc (3) |
