[Study Notes] file I/O operations on the Linux platform

The following functions are I/O (unbuffered I/O) functions without Caching:

For the kernel, all opened files are described by a non-negative integer (called a file descriptor ).

The following describes the file I/O functions:

(1) Open

This function is used to open or create a file. If the operation succeeds, the system returns the file descriptor. If the operation fails, the system returns-1.

Format:

# Include <sys/types. h>

# Include <sys/STAT. h>

# Include <fcntl. h>

Int open (const char * Name, int Oflag [| optional parameter] [, mode]);

(2) creat

This function creates a new file. If the operation succeeds, the system returns the file descriptor. If the operation fails, the system returns-1.

Format:

# Include <sys/types. h>

# Include <sys/STAT. h>

# Include <fcntl. h>

Int creat (const char * Name, mode_t mode );

(3) Close

This function is used to close a file that has already been called.

Format:

# Include <unistd. h>

Int close (INT file );

0 is returned. Otherwise,-1 is returned.

(4) lseek

This function is used to specify the displacement of the current file. This displacement is a non-negative integer used to indicate the number of bytes calculated from the beginning of the file.

Format:

# Include <unistd. h>

# Include <sys/types. h>

Off_t lseek (INT file, off_t offset, int whence );

The file displacement is returned successfully;-1 is returned if an error occurs.

(5) Reed

This function reads data from a file.

Format:

# Include <unistd. h>

Size_t read (INT file, void * Buf, size_t bytes );

Returns the byte book. If it has been read to the end, 0 is returned. If an error occurs,-1 is returned.

(6) Write

This function writes data to a file.

Format:

# Include <unistd. h>

Size_t write (INT file, void * buff, size_t bytes );

Returns the total number of bytes written to the file. The size must be smaller than the buffer capacity. -1 is returned if an error occurs.

(7) DUP

This function can be used to copy an existing file descriptor.

Format:

# Include <unistd. h>

Int DUP (INT oldfile );

Int duo2 (INT oldfile, int newfile); // you can specify the descriptor of the new file.

The file descriptor of the new file is returned successfully;-1 is returned if the file fails to be returned.

(8) fcntl

Purpose 1: copy the descriptor (cmd = f_duped)

Purpose 2: Get/set the identifier of the file's love Descriptor

Purpose 3: Get the File status flag

Purpose 4: Get/set the record lock

Purpose 5: Obtain/set asynchronous I/O

Format:

# Include <unistd. h>

# Include <fcntl. h>

Int fcntl (int fd, int cmd );

Int fcntl (int fd, int cmd, long Arg );

Int fcntl (

Int FD, int cmd, struct flock * Lock );

(9) IOCTL

This function is short for input/output control, that is, input/output control. It can control character devices through a file descriptor.

Format:

# Include <sys/IOCTL. h>

Int IOCTL (INT file, int request, char * argp | struct termios st );

0 is returned for success, and-1 is returned for error.