c - 我想知道 struct FILE 的内部成员，最新的

Question

当我读到 K&R 的 The C programming Language 第 176 页时，我非常兴奋。我找到了 struct FILE(我正在搜索的)的所有成员，知道它是如何工作的真是太棒了。但是你猜怎么着，gcc 提示说，错误:“FILE”没有名为“fd”的成员。这意味着现在情况发生了变化，我用谷歌搜索但找不到。请帮忙，提前谢谢你。

我可以使用 fileno() 来获取文件描述符，但我讨厌在抽象级别上工作。

int
main ( int argc, char **argv ){

    FILE *fp = fopen ("ct.c", "r");
    printf ("%i", fp->fd);

    return 0;
}

Answer 1

您需要查看 C 库的源代码。

既然你提到了 gcc 和 Linux，你可能正在使用 GNU libc，它当然是免费软件。

This file说:

/* The opaque type of streams.  This is the definition used elsewhere.  */
typedef struct _IO_FILE __FILE;

和this file声明 _IO_FILE 结构:

struct _IO_FILE {
  int _flags;       /* High-order word is _IO_MAGIC; rest is flags. */
#define _IO_file_flags _flags

  /* The following pointers correspond to the C++ streambuf protocol. */
  /* Note:  Tk uses the _IO_read_ptr and _IO_read_end fields directly. */
  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;
#if 0
  int _blksize;
#else
  int _flags2;
#endif
  _IO_off_t _old_offset; /* This used to be _offset but it's too small.  */

#define __HAVE_COLUMN /* temporary */
  /* 1+column number of pbase(); 0 is unknown. */
  unsigned short _cur_column;
  signed char _vtable_offset;
  char _shortbuf[1];

  /*  char* _save_gptr;  char* _save_egptr; */

  _IO_lock_t *_lock;
#ifdef _IO_USE_OLD_IO_FILE
};

上述内容可能来自“真正的”生产质量库，比 K&R 中使用的示例稍微复杂一些。而且，当然，您不能使用它，因为它是库内部的，FILE 是一种不透明类型，正如它所说的那样。