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What is data type of FILE in C?
In C we have used Files. To handle files, we use the pointer of type FILE. So the FILE is a datatype. This is called the Opaque datatype. So its implementation is hidden. The definition of the FILE is system specific. This is the definition of FILE in Ubuntu System −
FILE Definition
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
};Now let us see one example using FILE.
Text file (/tmp/test.txt): This is testing for fprintf... This is testing for fputs...
Example
#include <stdio.h>
main() {
FILE *fp;
char buff[255];
fp = fopen("/tmp/test.txt", "r");
fscanf(fp, "%s", buff);
printf("1 : %s
", buff );
fgets(buff, 255, (FILE*)fp);
printf("2: %s
", buff );
fgets(buff, 255, (FILE*)fp);
printf("3: %s
", buff );
fclose(fp);
}Output
1 : This 2: is testing for fprintf... 3: This is testing for fputs...
Updated on: 30-Jul-2019
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