Linux/C + +: File operations--open, read, write

Linux/C + +: File operations--open, create, close

File descriptor

Kernel (kernel) to access the file using the file descriptor (descriptor). The file descriptor is a non-negative integer. When you open an existing file or create a new file, the kernel returns a file descriptor. Read-write files also need to use file descriptors to specify which files to read and write. The system kernel maintains a list of file descriptors for each process. as follows:

The kernel Assignment file descriptor rule is that it is always allocated unused and is minimal. The first three file descriptors: 0, 1, 2, are already occupied by default. Of course, you can close it first. such as closing 1, redistribution, can lead to redirection.

Function prototypes

#include <fcntl.h>

int open (const char *path, int flag, .../*mode_t mode*/);

Function: Open File

Return value: Successful, returns the file descriptor; 1 If an error occurs

Parameters:

Path file paths

The open mode of the flag file

Common mode: o_rdonly read-only O_wronly Write only O_rdwr read/write o_exec perform O_search search (applies to directory) (must, five select one)

Optional: o_append append o_creat file does not exist, then create.

... File permissions

Function prototypes

#include <fcntl.h>

int Create (const char *path, mode_t mode);

Features: Creating files

Return value: Successful, returns the file descriptor; 1 If an error occurs

Parameters:

Path file paths

Mode file permissions

Function prototypes

#include <unistd.h>

int close (int fd);

Function: Close open files, release resources

Parameter: FD is pending file descriptor

Return: Success, return 0; error, return-1

It is necessary to note that when the process is finished, the kernel shuts down the files opened by the process.

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Linux/C + +: File operations--open, read, write