함수포인터

함수 포인터

함수의 이름도 주소이다.

#include<stdio.h>

void Func1(int a) {
	printf("Func1 %d\n", a);
}
int Func2() {
	printf("Func2\n");
	return 10;
}
int main() {

	void (*p)(int);
	p = Func1;
	(*p)(10);

	int (*q)();
	q = Func2;

	printf("%d", (*q)() + 100);

	return 0;
}

구조체 내에서 함수 포인터를 사용하여 아래와 같이 사용한다.

struct file_operations {
	struct module *owner;
	loff_t (*llseek) (struct file *, loff_t, int);
	ssize_t (*read) (struct file *, char __user *, size_t, loff_t *);
	ssize_t (*write) (struct file *, const char __user *, size_t, loff_t *);
	ssize_t (*read_iter) (struct kiocb *, struct iov_iter *);
	ssize_t (*write_iter) (struct kiocb *, struct iov_iter *);
	int (*iopoll)(struct kiocb *kiocb, struct io_comp_batch *,
			unsigned int flags);
	int (*iterate) (struct file *, struct dir_context *);
	int (*iterate_shared) (struct file *, struct dir_context *);
	__poll_t (*poll) (struct file *, struct poll_table_struct *);
	long (*unlocked_ioctl) (struct file *, unsigned int, unsigned long);
	long (*compat_ioctl) (struct file *, unsigned int, unsigned long);
	int (*mmap) (struct file *, struct vm_area_struct *);
	unsigned long mmap_supported_flags;
	int (*open) (struct inode *, struct file *);
	int (*flush) (struct file *, fl_owner_t id);
	int (*release) (struct inode *, struct file *);
	int (*fsync) (struct file *, loff_t, loff_t, int datasync);
	int (*fasync) (int, struct file *, int);
	int (*lock) (struct file *, int, struct file_lock *);
	ssize_t (*sendpage) (struct file *, struct page *, int, size_t, loff_t *, int);
	unsigned long (*get_unmapped_area)(struct file *, unsigned long, unsigned long, unsigned long, unsigned long);
	int (*check_flags)(int);
	int (*flock) (struct file *, int, struct file_lock *);
	ssize_t (*splice_write)(struct pipe_inode_info *, struct file *, loff_t *, size_t, unsigned int);
	ssize_t (*splice_read)(struct file *, loff_t *, struct pipe_inode_info *, size_t, unsigned int);
	void (*splice_eof)(struct file *file);
	int (*setlease)(struct file *, long, struct file_lock **, void **);
	long (*fallocate)(struct file *file, int mode, loff_t offset,
			  loff_t len);
	void (*show_fdinfo)(struct seq_file *m, struct file *f);
#ifndef CONFIG_MMU
	unsigned (*mmap_capabilities)(struct file *);
#endif
	ssize_t (*copy_file_range)(struct file *, loff_t, struct file *,
			loff_t, size_t, unsigned int);
	loff_t (*remap_file_range)(struct file *file_in, loff_t pos_in,
				   struct file *file_out, loff_t pos_out,
				   loff_t len, unsigned int remap_flags);
	int (*fadvise)(struct file *, loff_t, loff_t, int);
	int (*uring_cmd)(struct io_uring_cmd *ioucmd, unsigned int issue_flags);
	int (*uring_cmd_iopoll)(struct io_uring_cmd *, struct io_comp_batch *,
				unsigned int poll_flags);
} __randomize_layout;

 

간단한 예제로 작성해보자

#include <stdio.h>

// 구조체 정의: 함수 포인터를 멤버로 가지는 구조체
struct Hyndrome_operation {
    void (*act1)(int); // 함수 포인터 멤버
    void (*act2)(int); // 함수 포인터 멤버
};

// 함수 선언
void Func1(int x) {
    printf("Func1 : % d\n", x);
}

void Func2(int x) {
    printf("Func2 : %d\n", x);
}

int main() {
    // 구조체 변수 선언 및 선택적 초기화
    struct Hyndrome_operation hyops = {
        .act1 = Func1,
        .act2 = Func2,
    };

    // 함수 포인터를 멤버로 갖는 구조체의 함수 호출
    hyops.act1(10); // Func1 호출
    hyops.act2(20); // Func2 호출

    return 0;
}