[glibc] struct _IO_FILE

- glibc 2.29

 

> struct _IO_FILE

구조체는 /libio/bits/types/struct_FILE.h에 정의되어 있다.

 

struct _IO_FILE
{
  int _flags;        /* High-order word is _IO_MAGIC; rest is flags. */
 
  /* The following pointers correspond to the C++ streambuf protocol. */
  char *_IO_read_ptr;    /* Current read pointer */
  char *_IO_read_end;    /* End of get area. */
  char *_IO_read_base;    /* Start of putback+get area. */
  char *_IO_write_base;    /* Start of put area. */
  char *_IO_write_ptr;    /* Current put pointer. */
  char *_IO_write_end;    /* End of put area. */
  char *_IO_buf_base;    /* Start of reserve area. */
  char *_IO_buf_end;    /* End of reserve area. */
 
  /* The following fields are used to support backing up and undo. */
  char *_IO_save_base; /* Pointer to start of non-current get area. */
  char *_IO_backup_base;  /* Pointer to first valid character of backup area */
  char *_IO_save_end; /* Pointer to end of non-current get area. */
 
  struct _IO_marker *_markers;
 
  struct _IO_FILE *_chain;
 
  int _fileno;
  int _flags2;
  __off_t _old_offset; /* This used to be _offset but it's too small.  */
 
  /* 1+column number of pbase(); 0 is unknown. */
  unsigned short _cur_column;
  signed char _vtable_offset;
  char _shortbuf[1];
 
  _IO_lock_t *_lock;
#ifdef _IO_USE_OLD_IO_FILE
};
 
struct _IO_FILE_complete
{
  struct _IO_FILE _file;
#endif
  __off64_t _offset;
  /* Wide character stream stuff.  */
  struct _IO_codecvt *_codecvt;
  struct _IO_wide_data *_wide_data;
  struct _IO_FILE *_freeres_list;
  void *_freeres_buf;
  size_t __pad5;
  int _mode;
  /* Make sure we don't get into trouble again.  */
  char _unused2[15 * sizeof (int) - 4 * sizeof (void *) - sizeof (size_t)];
};

 

1. int _flags

상위 2바이트는 0xFBAD의 매직 워드를 가진다. (_IO_MAGIC)

하위 2바이트는 플래그 정보를 담고 있다. 플래그는 /libio/libio.h에 define 되어 있다.

 

/* Magic number and bits for the _flags field.  The magic number is
   mostly vestigial, but preserved for compatibility.  It occupies the
   high 16 bits of _flags; the low 16 bits are actual flag bits.  */
 
#define _IO_MAGIC         0xFBAD0000 /* Magic number */
#define _IO_MAGIC_MASK    0xFFFF0000
#define _IO_USER_BUF          0x0001 /* Don't deallocate buffer on close. */
#define _IO_UNBUFFERED        0x0002
#define _IO_NO_READS          0x0004 /* Reading not allowed.  */
#define _IO_NO_WRITES         0x0008 /* Writing not allowed.  */
#define _IO_EOF_SEEN          0x0010
#define _IO_ERR_SEEN          0x0020
#define _IO_DELETE_DONT_CLOSE 0x0040 /* Don't call close(_fileno) on close.  */
#define _IO_LINKED            0x0080 /* In the list of all open files.  */
#define _IO_IN_BACKUP         0x0100
#define _IO_LINE_BUF          0x0200
#define _IO_TIED_PUT_GET      0x0400 /* Put and get pointer move in unison.  */
#define _IO_CURRENTLY_PUTTING 0x0800
#define _IO_IS_APPENDING      0x1000
#define _IO_IS_FILEBUF        0x2000
                           /* 0x4000  No longer used, reserved for compat.  */
#define _IO_USER_LOCK         0x8000

 

2. char *_IO_read_ptr

읽기를 처리할 위치를 가리키는 포인터다.

 

3. char *_IO_read_end

읽을 데이터가 있는 영역의 끝을 가리키는 포인터다. EOF라고 보면 될 듯 하다.

 

4. char *_IO_read_base

읽고 있는 데이터의 시작을 가리키는 포인터다.

 

5. char *_IO_write_base

데이터를 쓸 영역의 시작 위치를 가리키는 포인터다.

 

6. char *_IO_write_ptr

현재 데이터를 쓸 곳을 가리키는 포인터다.

 

7. char *_IO_write_end

데이터를 쓸 영역의 끝을 가리키는 포인터다.

 

8. char *_IO_buf_base

버퍼의 시작 주소를 가리킨다.

 

9. char *_IO_buf_end

버퍼의 끝 주소를 가리킨다.

 

10. char *_IO_save_base

 

11. char *_IO_backup_base

 

12. char *_IO_save_end

 

13. struct _IO_marker *_markers

 

14. struct _IO_FILE *_chain

 

15. int _fileno

 

16. int _flags2

 

17. __off_t _old_offset

 

18. unsigned short _cur_column

 

19. signed char _vtable_offset

 

19. char _shortbuf[1]

 

20. _IO_lock_t *_lock

 

21. struct _IO_codecvt *_codecvt

 

22. struct _IO_wide_data *_wide_data

 

23. struct _IO_FILE *_freeres_list

 

24. void *_freeres_buf

 

25. size_t __pad5

 

26. char _unused2[15 * sizeof(int) - 4 * sizeof(void *) - sizeof(size_t)]

 

glibc 코드 진짜 그지같다 읽는게 너무 힘들다