The standard input and output follow the rules and several functions of fileno, freopen, fdopen, ftell, fseek, and rewind.

/*
========================================================== ==========================================
Name: quanhaunchong. c
Author:
Version:
Copyright: Your copyright notice
Description: Hello world in C, ANSI-style
========================================================== ==========================================
*/

# Include <stdio. h> // standard I/O library, fully buffered
# Include <stdlib. h>
// All Input and Output Using the stdio library must meet the full buffering, row buffering, and non-buffering rules.
// Full Buffer: only when the buffer content is full can the file be written, but the buffer content will be forcibly written into the file to be written in the case of return
// Row Buffer: When '\ n' is encountered, the buffer content is written to the specified file
// No buffer: This is especially used for stderr. When a standard error is output, the standard input and output are written directly without passing through the buffer.
Int main (void ){
// Full Buffer
Printf ("helloworld ");
// Fflush (stdout); // if not satisfied, the standard output is included. This is the solution to full buffering.


// Row Buffer
Printf ("helloworld \ n ");
Int I;
For (I = 0; I <2; I ++)
{
Printf ("helloworl ");
}
// No buffer. The output text is red and displayed as an error.
Fputs ("hell9", stderr );
While (1 );
Return exit_success; // when the process exits, the buffer content is forcibly refreshed to the file to be written.
}

Fdopen:

	Fdopen (convert file description to file pointer)
Related functions	Fopen, open, fclose
Header file	# Include <stdio. h>
Define functions	File * fdopen (INT Fildes, const char * mode );
Function Description	Fdopen () converts the file description of Fildes to the corresponding file pointer and returns the result. The mode string represents the stream format of the file pointer, which must be the same as the read/write mode of the original file description. For more information about the mode string format, see fopen ().
Return Value	Returns the file pointer to the stream when the conversion is successful. If the Error Code fails, null is returned, and the error code is stored in errno.
Example	# Include <stdio. h> Main () { File * fp = fdopen (0, "W + "); Fprintf (FP, "% s \ n", "hello !"); Fclose (FP ); }
Run	Hello!

Freopen:

	Freopen (open a file)
Related functions	Fopen, fclose
Header file	# Include <stdio. h>
Define functions	File * freopen (const char * path, const char * mode, file * stream );
Function Description	The parameter path string contains the path and file name of the file to be opened. For details about the parameter mode, see fopen. The stream parameter is an opened file pointer. Freopen () will close the file stream opened by the original stream, and then open the file with the path parameter.
Return Value	After the file is successfully opened, the file pointer pointing to the stream will be returned. If the file fails to be opened, null is returned and the error code is stored in errno.
Example	# Include <stdio. h> Main () { File * FP; Fp = fopen ("/etc/passwd", "R "); Fp = freopen ("/etc/group", "R", FP ); Fclose (FP ); }

Fileno:

	Fileno (returns the file description used by the file Stream)
Related functions	Open, fopen
Header file	# Include <stdio. h>
Define functions	Int fileno (File * stream );
Function Description	Fileno () is used to obtain the file description used by the file stream specified by the parameter stream.
Return Value	Returns the description of a file.
Example	# Include <stdio. h> Main () { File * FP; Int FD; Fp = fopen ("/etc/passwd", "R "); FD = fileno (FP ); Printf ("FD = % d \ n", FD ); Fclose (FP ); }
Run	FD = 3

/*
========================================================== ==========================================
Name: CDX. c
Author:
Version:
Copyright: Your copyright notice
Description: Hello world in C, ANSI-style
========================================================== ==========================================
*/

# Include <stdio. h>
# Include <stdlib. h>
# Include <sys/types. h>
# Include <sys/STAT. h>
# Include <fcntl. h>
Int main (void ){
File * fp = NULL;

// Redirect cat main. c> TXT: input the content in Mian and C to the TXT file.
Fp = fopen ("hello.txt", "W ");
If (FP = NULL)
{
Perror ("Open error ");
Return 0;
}
// Fp = freopen ("/etc/group", "R", FP );
Freopen ("world.txt", "W +", FP );
Fputs ("helloweotd", FP );

// Fieno
Int FD;
FD = fileno (FP );
Printf ("FD = % d \ n", FD );
Fclose (FP );
File * FP1 = fdopen (0, "W + ");
Fprintf (FP1, "% s \ n", "Hello! ");
// Puts ("!!! Hello world !!! ");/* Prints !!! Hello world !!! */
Return exit_success;
}

Ftell:

	Ftell (get the reading location of the file stream)
Related functions	Fseek, rewind, fgetpos, fsetpos
Header file	# Include <stdio. h>
Define functions	Long ftell (File * stream );
Function Description	Ftell () is used to obtain the current read/write location of a file stream. The stream parameter is an opened file pointer.
Return Value	If the call is successful, the current read/write location is returned. If an error occurs,-1 is returned, and errno stores the error code.
Error Code	The file stream of the ebadf parameter is invalid or can be read and written at a movable location.
Example	See fseek ().

Fseek:

	Fseek (read/write location of a mobile file Stream)
Related functions	Rewind, ftell, fgetpos, fsetpos, lseek
Header file	# Include <stdio. h>
Define functions	Int fseek (File * stream, long offset, int whence );
Function Description	Fseek () is used to move the read/write location of a file stream. The stream parameter is an opened file pointer, And the offset parameter is the number of read/write locations to be moved Based on the whence parameter.
Parameters	Whence is one of the following: The offset displacement from the beginning of the seek_set file is the new read/write location. Seek_cur increases the offset displacement at the current read/write position. Seek_end points the read/write position to the end of the file and then increases the offset displacement. When the whence value is seek_cur or seek_end, the offset parameter allows negative values. The following are special usage methods: 1) to move the read/write location to the beginning of the file: fseek (File * stream, 0, seek_set ); 2) to move the read/write location to the end of the file: fseek (File * stream, 0, 0seek_end );
Return Value	If the call is successful, 0 is returned. If an error exists,-1 is returned. errno stores the error code.
Additional instructions	Unlike lseek (), fseek () returns a read/write location. Therefore, ftell () must be used to obtain the current read/write location.

Rewind:

	Rewind (resetting the file stream's read/write position to start with the file)
Related functions	Fseek, ftell, fgetpos, fsetpos
Header file	# Include <stdio. h>
Define functions	Void rewind (File * stream );
Function Description	Rewind () is used to move the read/write location of the file stream to the beginning of the file. The stream parameter is an opened file pointer. This function is equivalent to calling fseek (stream, 0, seek_set ).
Return Value
Example	Refer to fseek ()

# Include <stdio. h>
# Include <stdlib. h>
# Include <sys/types. h>
# Include <sys/STAT. h>
# Include <fcntl. h>

Int main (INT argc, char ** argv ){
// Function: fseek (File * stream, long off_set, int wherece) can move the file pointer to the specified position in the file.
// Long ftell (File * stream, fpos_t * POS );
File * FP;
Int I;
Char Buf [9] [10];
Fp = fopen ("/home/wzm/workspace1/filesuiji/src/TAB. dat", "R ");
If (FP = NULL)
{
Perror ("Open error ");
Return-1;
}
// Move the file pointer to 30 locations
Fseek (FP, 30, seek_set );
// Output the current pointer position
Printf ("current file position [% ld] \ n", ftell (FP ));
For (I = 0; I <6; I + = 3)
{
Fscanf (FP, "% 10 S % 10 S % 10s \ n", Buf [I], Buf [I + 1], Buf [I + 2]);
Printf (FP, "% S % s \ n", Buf [I], Buf [I + 1], Buf [I + 2]);
}
Fclose (FP );
Return exit_success;
}