En langage C, quel est le type de données de FILE ?

En langage C, nous utilisons des fichiers (Files) pour gérer les opérations sur les fichiers, et nous utilisons des pointeurs de type FILE pour faire fonctionner les fichiers. Par conséquent, FILE est un type de données. C'est ce qu'on appelle un type de données opaque car son implémentation est cachée. La définition de FILE est spécifique au système. Voici la définition de FILE dans le système Ubuntu :

Définition de 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
};

Regardons maintenant un exemple d'utilisation de FILE. La traduction chinoise de

Text file (/tmp/test.txt):
This
is testing for fprintf...
This is testing for fputs...

Example

est :

Example

#include <stdio.h>
main() {
   FILE *fp;
   char buff[255];
   fp = fopen("/tmp/test.txt", "r");
   fscanf(fp, "%s", buff);
   printf("1 : %s</p><p>", buff );
   fgets(buff, 255, (FILE*)fp);
   printf("2: %s</p><p>", buff );
   fgets(buff, 255, (FILE*)fp);
   printf("3: %s</p><p>", buff );
   fclose(fp);
}

Output

1 : This
2: is testing for fprintf...

3: This is testing for fputs...

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