From e0f8cdb3d3b8d8f513f90a9fbab51511c4779db7 Mon Sep 17 00:00:00 2001
From: Jet Hughes <jethughes0@gmail.com>
Date: Thu, 11 Aug 2022 11:39:21 +1200
Subject: [PATCH] vault backup: 2022-08-11 11:39:21

---
 .../notes/10-intro-to-c-arrays-malloc-free.md | 32 ++++++++++++++++++-
 1 file changed, 31 insertions(+), 1 deletion(-)

diff --git a/content/notes/10-intro-to-c-arrays-malloc-free.md b/content/notes/10-intro-to-c-arrays-malloc-free.md
index fafa0db7f..b5390e723 100644
--- a/content/notes/10-intro-to-c-arrays-malloc-free.md
+++ b/content/notes/10-intro-to-c-arrays-malloc-free.md
@@ -62,6 +62,36 @@ uint_t byte_array[1024];
 
 ## malloc
 - "memory allocate"
-- 
+- always in bytes
+
+```c
+uint8_t *space = malloc(16); //give me 16 bytes of space
+uint64_t *block = malloc(sizeof(*uint64_t) * 16);
+uint64_t *another = malloc(sizeof(*another) * 16); //better: can change type without breaking it
+```
 
 
+## free
+**when you have finished using an allocated block you must free that block**
+
+```c
+uint64_t *block = malloc(sizeof(*block) * 16); //better: can change type without breaking it
+//do something
+free(block);
+```
+
+- never free memory you didn't allocate
+- never free the same memory twice
+- must call free before you lose the pointer to the block of memory
+
+## bugs
+- malloc'd block is too small
+	- buffer-overrun
+- didn't free a block
+	- memory leak
+- malloc and free small units a large number of times
+	- memory fragmentation
+- free same block more than once
+	- corrupt memory management routines
+- using memory after it has been freed
+	- it have been re-used by malloc
\ No newline at end of file