defer in C (gcc only)

defer.c

#include <stdio.h>
#include <fcntl.h>
#include <sys/types.h>
#include <unistd.h>

#define CAT_IMPL(x, y) x##y
#define CAT(x, y) CAT_IMPL(x, y)

#define defer DEFER_IMPL(CAT(defer__, __COUNTER__))
#define DEFER_IMPL(name) auto void name (void*); \
	int __attribute__ ((cleanup(name))) CAT(name, _var) = 42; \
	void name (void*)

void foo()
{
	int passwd_fd = open("/etc/passwd", O_RDONLY);
	defer {
		close(passwd_fd);
		printf("closed passwd fd\n");
	}
	int group_fd = open("/etc/group", O_RDONLY);
	defer {
		close(group_fd);
		printf("closed group fd\n");
	}
	printf("bye from foo()\n");
}

int main(void)
{
	foo();

	return 0;
}

% gcc -Wall -Wextra -std=c23 -o defer defer.c && ./defer
bye from foo()
closed group fd
closed passwd fd