A simple Garbage Collector in C.
The function gc_get_ptr_list() avoids a global variable...
The function gc_alloc_ptr_list avoids to alloc the pointer with the desired size + sizeof(void *), explanation:
Let's say I want to allocate a char * for 5 characters (word "test\0")
Memory allocated for user
|
+-------+
| |
+-+-+-+-+-+
|T|E|S|T|█|
+-+-+-+-+-+
↑
Address given to the user
Well, in reality I'm going to allocate 5 + sizeof (void *), to get that:
Memory allocated for user
|
+-------+
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+
| | | | | | | | |T|E|S|T|█|
+-+-+-+-+-+-+-+-+-+-+-+-+-+
↑ ↑
| Address given to the user
|
Previous pointer address
The first 8 bytes will be used to store the previous allocated address I assign with the same function -> linked list!
With the particularity of having the attributes __attribute__ ((destructor)) causes the function to be called automatically after execution enters main(). All stored pointers in the list are free at the end of the program.
Graphically explanation:
0 The first allocation points to nothing (NULL / 0)
↑
|
|
| Memory allocated in addition by the GC to store the address of the previous allocation
| | Allocated memory requested by the user
| | |
|+-------------+ +-------+
|| | | |
+-+-+-+-+-+-+-+-+-+-+-+-+-+
42 |0|0|0|0|0|0|0|0|T|E|S|T|█|
+-+-+-+-+-+-+-+-+-+-+-+-+-+
↑ ↑
| Address given to the user (42 + 8)
|
| Memory allocated in addition by the GC to store the address of the previous allocation
| | Allocated memory requested by the user
| | |
|+-------------+ +-----+
|| | | |
+-+-+-+-+-+-+-+-+-+-+-+-+
113 |4|2|0|0|0|0|0|0|O|U|I|█|
+-+-+-+-+-+-+-+-+-+-+-+-+
↑ ↑
| Address given to the user (113 + 8)
|
| Memory allocated in addition by the GC to store the address of the previous allocation
| | Allocated memory requested by the user
| | |
|+-------------+ +---------------+
|| | | |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
189 |1|1|3|0|0|0|0|0|T|O|T|O|T|A|T|A|█|
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
↑
Address given to the user (189 + 8)