Node.js fs.filehandle.fd()用法及代码示例

fs.filehandle.fd()方法是文件系统模块中fs.filehandle类的内置应用程序编程接口，用于提供此文件句柄对象的数字文件描述符。

用法:

const filehandle.fd()

参数：此方法不接受任何参数。

返回值：此方法返回此文件句柄对象的数字文件描述符。

以下示例程序旨在说明Node.js中fs.filehandle.fd()方法的使用：

范例1： 文件名：index.js

// Node.js program to demonstrate the  
// filehandle.fd() method 
const fs = require('fs'); 
const fsPromises = fs.promises; 
  
console.log("content of file before operation:- "
            + (fs.readFileSync('example.txt'))); 
  
// Initiating asyncrionise function 
async function funct() { 
  
    // Initializng filehandle 
    let filehandle = null; 
    let value = null; 
  
    try { 
  
        // Creating and initiating  filehandle 
        filehandle = await  
            fsPromises.open('example.txt', 'r+'); 
  
        // Getting the Numeric file descriptor 
        // by using fd api 
        value = filehandle.fd; 
  
    } finally { 
  
        if (filehandle) { 
  
            // Close the file if it is opened. 
            console.log( 
                "Numeric file descriptor:- " + value); 
            console.log( 
                "content of file after operation:- " + 
                (fs.readFileSync('example.txt'))); 
  
            await filehandle.close(); 
        } 
    } 
} 
  
funct().catch(console.error);

运行程序之前的目录结构：

运行程序后的目录结构：

使用以下命令运行index.js文件：

node index.js

输出：

content of file before operation:- ABCD
Numeric file descriptor:- 3
content of file after operation:- ABCD

范例2：
文件名：index.js

// Node.js program to demonstrate the  
// filehandle.fd() method 
const fs = require('fs'); 
const fsPromises = fs.promises; 
  
// Data for the new file 
let data = "This is a file containing "
            + "a collection of books."; 
  
// Name of the file to be created 
let file = "books.txt"; 
  
// Creating the new file 'books.txt' 
fs.writeFile(file, data, (err) => { 
  
    // Cathing error 
    if (err) { 
        console.log(err); 
    } 
}); 
  
// Using fs.exists() method  
fs.exists(file, (exists) => { 
    if (exists) { 
        console.log("content of file "
            + "before operation:- " 
            + (fs.readFileSync(file))); 
    } 
}); 
  
// Initiating asyncrionise function 
async function funct() { 
  
    // Initializng filehandle 
    let filehandle = null; 
  
    try { 
  
        // Creating and initiating  filehandle 
        filehandle = await  
                fsPromises.open(file, 'r+'); 
  
        // Getting the Numeric file descriptor 
        // by using fd api 
        value = filehandle.fd; 
  
    } finally { 
  
        if (filehandle) { 
  
            // Close the file if it is opened. 
            console.log( 
                "Numeric file descriptor:- " 
                + value); 
                  
            console.log("content of file "
                + "after operation:- " 
                + (fs.readFileSync(file))); 
  
            await filehandle.close(); 
        } 
    } 
} 
  
funct().catch(console.error);

运行程序之前的目录结构：

运行程序后的目录结构：

使用以下命令运行index.js文件：

node index.js

输出：

content of file before operation:- This is a file containing a collection of books.
Numeric file descriptor:- 4
content of file after operation:- This is a file containing a collection of books.

参考： https://nodejs.org/dist/latest-v12.x/docs/api/fs.html#fs_filehandle_fd

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注：本文由纯净天空筛选整理自RohitPrasad3大神的英文原创作品 Node.js fs.filehandle.fd() Method。非经特殊声明，原始代码版权归原作者所有，本译文未经允许或授权，请勿转载或复制。