Linux system programming files and I/O (i) File open shutdown

First, file descriptor

For Linux, all operations on a device or file are performed through a file descriptor. When you open or create a file, the kernel returns a file descriptor (Non-negative integer) to the process. Subsequent operations on the file require only the file descriptor, and the kernel records information about the open file (the file structure body).

When a process starts, 3 files are opened by default, standard input, standard output, standard error, the corresponding file descriptor is 0 (Stdin_fileno), 1 (Stdout_fileno), 2 (Stderr_fileno), and these constants are defined in the Unistd.h header file.

Fileno: Converts a file pointer to a file descriptor

Fdopen: Converts a file descriptor to a file pointer

Second, what is I/O

Input/output is the process of copying data between main memory and external devices

Device-> memory (input operation)

Memory-> device (output operation)

Advanced I/O

The standard I/O libraries provided by ANSI C are called Advanced I/O, and are often referred to as buffered I/O

Low-level I/O

Usually also called I/O without buffering

Third, the opening of the file closed

Open System call 1:

Function prototypes

int open (const char *path, int flags);

Parameters

Path: The name of the file, which can contain (absolute and relative) paths

Flags: File open mode

return value:

Open success, return file descriptor, open failed, return-1

Open System Call 2:

Function prototypes

int open (const char *path, int flags,mode_t mode);

Parameters

Path: The name of the file, which can contain (absolute and relative) paths

Flags: File open mode