Use-after-free

Use-after-free

Designed by	User:RaiseAfloppaFan3925
Appeared in	Category:2026
Computational class	Below combinational logic?
Reference implementation	Unimplemented
Influenced by	Malloc, Double free, Mixed allocators

Use-after-free is an esoteric programming language by User:RaiseAfloppaFan3925 in 2026 based on the undefined behavior of using a pointer after freeing it in C. It can be considered a superset of Malloc.

Double free is used as the base for the syntax and semantics of Use-after-free. If you haven't understood Double free then you likely won't be able to understand Use-after-free.

Functions

There are malloc and free.

printf exists too and is just C's printf.

The peek function reads a single byte from memory.

?! message
message : "Hello, world!"
printf "peek message = %c\n" peek message

Output:

peek message = H

The poke function overrides a single byte in memory.

?! ptr
ptr : malloc sizeof(char)
poke ptr 123
printf "%d\n" ` ptr
poke ptr -98
printf "%d\n" ` ptr

Output:

123
-98

There are also variants of both peek and poke for different types in C. However, for peek, only the integer type ones are actually useful for computation as everything else would raise a type error if you tried to assign them to a variable since non-integer types cannot be casted into void* and the only usable variable type is void* as denoted by ?!.

Peek	Poke	C type
peek and peekuc	poke and pokeuc	char and unsigned char
peeks and peekus	pokes and pokeus	short and unsigned short
peeki and peeku	pokei and pokeu	int and unsigned int
peekl and peekul	pokel and pokeul	long and unsigned long
peekll and peekull	pokell and pokeull	long long and unsigned long long
peekf	pokef	float
peekd	poked	double
peekld	pokeld	long double
peekp	pokep	void*

Examples

"Hello, world!" program

printf "Hello, world!\n"

XKCD Random Number

?! comment
comment : "Chosen by fair dice roll."
printf "4\n"

Use-after-free error

?! value
value : malloc sizeof(int)
pokei value ` 8
free value
printf "%d\n" ` value

Something very bad that you should not do

?! tmp
free free
free (poke (malloc 10))
free "Hello, world!\n"
free printf
tmp : malloc
malloc : "a"
free malloc
malloc : tmp
free malloc

See also

• Malloc
• Double free, the language used as a base for this one
• Mixed allocators