Home Operation and Maintenance Linux Operation and Maintenance Detailed introduction to file descriptors and file pointers under Linux

Detailed introduction to file descriptors and file pointers under Linux

Jun 02, 2017 am 09:56 AM

This article mainly introduces the detailed information about file descriptors and file pointers under Linux. Friends in need can refer to

File descriptors under Linux Descriptors and file pointers

File identifier:

First of all, let’s understand what a file identifier is?

File description A symbol is a term in computer science and is an abstract concept used to express a reference to a file. In Linux, each process will save a file descriptor table in the process control block (PCB). The file descriptor is the

index

of this table. Each table has There is a pointer to the open file. Each Linux process should have three standard file descriptors, corresponding to three standard streams.

IntegerValueConstant0Standard inputFILE ##1Standard outputSTDOUT_FILENOstdout2Standard errorSTDERR_FILENOstderr opens an existing file or creates a new file, the kernel returns a file descriptor to the process. In programming, some low-level programming often revolves around file descriptors. However, the concept of file descriptors is often only applicable to operating systems such as UNIX and Linux.
Name(unistd.h)Symbol (stdio.h)File stream
STDIN_NO stdin
The file descriptor is at Formally it is a non-negative integer. In fact, it is an index value pointing to the record table of files opened by the process maintained by the kernel for each process. When a program

Operations related to file descriptors:


Function

Operation

Operations related to a single file descriptorendchmod(), etc. With file descriptors Table correlation operationsFile pointer:The file pointer is what we learn in C language
File descriptor generation open(), socket(), pipe(), etc.
read(), write(), s(), f
Operations related to plural file descriptorsselect(), poll(), etc.
close(), dup(), etc.
. In C language, a pointer

variablepoints to a file. This pointer is called a file pointer. Through the file pointer, we can perform various operations on the pointed file. The C language uses file pointers instead of file descriptors as I/O handles. The file pointer points to a data structure called the FILE structure in the user area of ​​the process. The FILE structure contains a buffer and a file descriptor.
The file pointer is a common format of C language, so it is relatively easier to transplant.

We usually obtain the file pointer:

1

<a href="https://www.php.cn/wiki/1499.html" target="_blank">FILE *fp = fopen("test.txt","r");</a>

After obtaining the pointer, We can get the information of the file descriptor in the pointer. The file descriptor is unique, but the file pointer is not unique. The

object

pointed to by the file pointer is unique.

Conversion of file descriptors and file pointers:

1

2

3

int fileno(FILE *stream);

 

FILE *fdopen(int fd,const char *mode);

Copy after login

The first parameter of fdopen is an open file descriptor, and mode indicates the opening methodString, the same as fopen, such as "w" or "r".

filenoFunction, it returns the file descriptor corresponding to the file stream, and returns - on failure 1.

The above is the detailed content of Detailed introduction to file descriptors and file pointers under Linux. For more information, please follow other related articles on the PHP Chinese website!

Statement of this Website
The content of this article is voluntarily contributed by netizens, and the copyright belongs to the original author. This site does not assume corresponding legal responsibility. If you find any content suspected of plagiarism or infringement, please contact admin@php.cn

Hot AI Tools

Undresser.AI Undress

Undresser.AI Undress

AI-powered app for creating realistic nude photos

AI Clothes Remover

AI Clothes Remover

Online AI tool for removing clothes from photos.

Undress AI Tool

Undress AI Tool

Undress images for free

Clothoff.io

Clothoff.io

AI clothes remover

Video Face Swap

Video Face Swap

Swap faces in any video effortlessly with our completely free AI face swap tool!

Hot Tools

Notepad++7.3.1

Notepad++7.3.1

Easy-to-use and free code editor

SublimeText3 Chinese version

SublimeText3 Chinese version

Chinese version, very easy to use

Zend Studio 13.0.1

Zend Studio 13.0.1

Powerful PHP integrated development environment

Dreamweaver CS6

Dreamweaver CS6

Visual web development tools

SublimeText3 Mac version

SublimeText3 Mac version

God-level code editing software (SublimeText3)

What computer configuration is required for vscode What computer configuration is required for vscode Apr 15, 2025 pm 09:48 PM

VS Code system requirements: Operating system: Windows 10 and above, macOS 10.12 and above, Linux distribution processor: minimum 1.6 GHz, recommended 2.0 GHz and above memory: minimum 512 MB, recommended 4 GB and above storage space: minimum 250 MB, recommended 1 GB and above other requirements: stable network connection, Xorg/Wayland (Linux)

Linux Architecture: Unveiling the 5 Basic Components Linux Architecture: Unveiling the 5 Basic Components Apr 20, 2025 am 12:04 AM

The five basic components of the Linux system are: 1. Kernel, 2. System library, 3. System utilities, 4. Graphical user interface, 5. Applications. The kernel manages hardware resources, the system library provides precompiled functions, system utilities are used for system management, the GUI provides visual interaction, and applications use these components to implement functions.

How to run java code in notepad How to run java code in notepad Apr 16, 2025 pm 07:39 PM

Although Notepad cannot run Java code directly, it can be achieved by using other tools: using the command line compiler (javac) to generate a bytecode file (filename.class). Use the Java interpreter (java) to interpret bytecode, execute the code, and output the result.

vscode cannot install extension vscode cannot install extension Apr 15, 2025 pm 07:18 PM

The reasons for the installation of VS Code extensions may be: network instability, insufficient permissions, system compatibility issues, VS Code version is too old, antivirus software or firewall interference. By checking network connections, permissions, log files, updating VS Code, disabling security software, and restarting VS Code or computers, you can gradually troubleshoot and resolve issues.

vscode terminal usage tutorial vscode terminal usage tutorial Apr 15, 2025 pm 10:09 PM

vscode built-in terminal is a development tool that allows running commands and scripts within the editor to simplify the development process. How to use vscode terminal: Open the terminal with the shortcut key (Ctrl/Cmd). Enter a command or run the script. Use hotkeys (such as Ctrl L to clear the terminal). Change the working directory (such as the cd command). Advanced features include debug mode, automatic code snippet completion, and interactive command history.

How to check the warehouse address of git How to check the warehouse address of git Apr 17, 2025 pm 01:54 PM

To view the Git repository address, perform the following steps: 1. Open the command line and navigate to the repository directory; 2. Run the "git remote -v" command; 3. View the repository name in the output and its corresponding address.

Where to write code in vscode Where to write code in vscode Apr 15, 2025 pm 09:54 PM

Writing code in Visual Studio Code (VSCode) is simple and easy to use. Just install VSCode, create a project, select a language, create a file, write code, save and run it. The advantages of VSCode include cross-platform, free and open source, powerful features, rich extensions, and lightweight and fast.

Can vscode be used for mac Can vscode be used for mac Apr 15, 2025 pm 07:36 PM

VS Code is available on Mac. It has powerful extensions, Git integration, terminal and debugger, and also offers a wealth of setup options. However, for particularly large projects or highly professional development, VS Code may have performance or functional limitations.

See all articles