linux FILE 类型.

　　stdio.h 头文件中,有以下内容(用内部行号解释):

 1 /* The opaque type of streams.  This is the definition used elsewhere.  */

 2  46 typedef struct _IO_FILE FILE;

 3 ...

 4 #include <libio.h>

 5 ...

 6 /* Standard streams.  */

 7 142 extern struct _IO_FILE *stdin;          /* Standard input stream.  */

 8 143 extern struct _IO_FILE *stdout;         /* Standard output stream.  */

 9 144 extern struct _IO_FILE *stderr;         /* Standard error output stream.  */145 #ifdef __STDC__

10 146 /* C89/C99 say they're macros.  Make them happy.  */

11 147 #define stdin stdin

12 148 #define stdout stdout

13 149 #define stderr stderr

14 150 #endif

　　由上,知道 FILE 是 struct _IO_FILE 类型的别名,或者说 FILE 类型就是 struct _IO_FILE 类型,由 第143行中的 _IO_FILE,往上追溯至 include 预处理指令,我们可以在 libio.h 头文件中看到 _IO_FILE 结构体的定义:

 1 struct _IO_FILE {

 2 269   int _flags;           /* High-order word is _IO_MAGIC; rest is flags. */

 3 270 #define _IO_file_flags _flags

 4 271

 5 272   /* The following pointers correspond to the C++ streambuf protocol. */

 6 273   /* Note:  Tk uses the _IO_read_ptr and _IO_read_end fields directly. */

 7 274   char* _IO_read_ptr;   /* Current read pointer */

 8 275   char* _IO_read_end;   /* End of get area. */

 9 276   char* _IO_read_base;  /* Start of putback+get area. */

10 277   char* _IO_write_base; /* Start of put area. */

11 278   char* _IO_write_ptr;  /* Current put pointer. */

12 279   char* _IO_write_end;  /* End of put area. */

13 280   char* _IO_buf_base;   /* Start of reserve area. */

14 281   char* _IO_buf_end;    /* End of reserve area. */

15 282   /* The following fields are used to support backing up and undo. */

16 283   char *_IO_save_base; /* Pointer to start of non-current get area. */

17 284   char *_IO_backup_base;  /* Pointer to first valid character of backup area     */

18 285   char *_IO_save_end; /* Pointer to end of non-current get area. */

19 286

20 287   struct _IO_marker *_markers;

21 288

22 289   struct _IO_FILE *_chain;

23 

24 291   int _fileno;

25 292 #if 0

26 293   int _blksize;

27 294 #else

28 295   int _flags2;

29 296 #endif

30 297   _IO_off_t _old_offset; /* This used to be _offset but it's too small.  */

31 298

32 299 #define __HAVE_COLUMN /* temporary */

33 300   /* 1+column number of pbase(); 0 is unknown. */

34 301   unsigned short _cur_column;

35 302   signed char _vtable_offset;

36 303   char _shortbuf[1];

37 304

38 305   /*  char* _save_gptr;  char* _save_egptr; */

39 306

40 307   _IO_lock_t *_lock;

41 308 #ifdef _IO_USE_OLD_IO_FILE

42 309 };

　　稍微注意的是(外侧行号解释), stdio.h 头文件中的第 4行优先于第 2 行执行,虽然第2行在第4行的前面.