C 第2000章: 文件

文件

FILE

 

FILE结构定义：

typedef struct _IO_FILE FILE;

 

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
};

struct _IO_FILE_complete
{
  struct _IO_FILE _file;
#endif
#if defined _G_IO_IO_FILE_VERSION && _G_IO_IO_FILE_VERSION == 0x20001
  _IO_off64_t _offset;
# if defined _LIBC || defined _GLIBCPP_USE_WCHAR_T
  /* Wide character stream stuff.  */
  struct _IO_codecvt *_codecvt;
  struct _IO_wide_data *_wide_data;
  struct _IO_FILE *_freeres_list;
  void *_freeres_buf;
  size_t _freeres_size;
# else
  void *__pad1;
  void *__pad2;
  void *__pad3;
  void *__pad4;
  size_t __pad5;
# endif
  int _mode;
  /* Make sure we don't get into trouble again.  */
  char _unused2[15 * sizeof (int) - 4 * sizeof (void *) - sizeof (size_t)];
#endif
};

文件操作

 

打开模式

打开文件调用fopen函数的时候第2个参数需要指定一个模式，这个模式并不是要打开的磁盘上的文件的模式。在FILE中，也就是struct _IO_FILE结构体中有一个_mode成员，调用fopen的时候会指定_mode。

 

打开文件

fopen

函数原型

FILE * fopen ( const char * filename, const char * mode );

 

创建文件

创建文件也是调用fopen函数。如果文件不存在，打开模式mode只要指定了"w","a"，包括"w+","a+"，都会创建文件。

 

#include <stdio.h>
int main(int argc, char* argv[])
{
  FILE *fp;
  if (argc != 2)
  {
    printf("invalid args.\n");
    return 1;
  }
  fp = fopen(argv[1], "w");
  if (! fp)
  {
    printf("fopen err.\n");
    return 1;
  }
  fclose(fp);
  return 0;
}

读写

 

 

 

读写位置

 

fpos_t

#ifndef __USE_FILE_OFFSET64
typedef _G_fpos_t fpos_t;
#else
typedef _G_fpos64_t fpos_t;
#endif

_G_fpos_t

typedef struct
{
  __off_t __pos;
  __mbstate_t __state;
} _G_fpos_t;

_G_fpos64_t

typedef struct
{
  __off64_t __pos;
  __mbstate_t __state;
} _G_fpos64_t;

获取读写位置

fgetpos

函数原型

int fgetpos ( FILE * stream, fpos_t * pos );

 

ftell

函数原型

long int ftell ( FILE * stream );

 

设置读写位置

通过fsetpos，fseek都可以设置读写位置。

fsetpos

函数原型

int fsetpos ( FILE * stream, const fpos_t * pos );

 

fseek

函数原型

int fseek ( FILE * stream, long int offset, int origin );

 

读取文件

 

写入文件