Node.js fs.writeSync()方法
原文:https://www.geeksforgeeks.org/node-js-fs-writesync-method/
文件系统模块或 fs 模块是 Node js 中的一个内置模块，用于处理计算机上的文件。模块的功能可以通过导入 fs 模块来使用。文件系统模块的 fs.writeSync()函数是 write()方法的同步版本，可以将 fs 模块包含在程序中。它可以用于将文本和二进制数据写入文件。
语法:
fs.writeSync( fd, string, position, encoding )
或者
fs.writeSync( fd, buffer, offset, length, position )
参数:
- fd: 代表文件描述符，它是一个标识文件的数字。我们可以使用 fs.openSync()方法，并在其中传递一个描述文件位置的字符串，它将返回一个整数，即文件描述符。
- 字符串:是将要写入文件的字符串。
- 位置:指定文件中要写入文本的位置。如果在方法中没有传递位置或者没有使用整数值来指定位置，那么它将从第 0 个位置开始写入。如果已经在该位置写入了字符串，则该方法将覆盖在该位置传递的新字符串。
- 编码:是指定字符编码的字符串。默认情况下，它是 utf8。
- 缓冲区:包含缓冲区类型值，如缓冲区、类型化数组、数据视图。
- 偏移量:是一个整数值，指定缓冲区中要写入文件的部分。
- 长度:是一个整数值，指定写入文件的字节数。
返回值:返回写入的字节数。
示例:
index.js
// Importe fs module
const fs = require("fs");
// Create a file input.txt and open it
// using openSync
// The second parameter is the flag
// which is r+ used for reading and
// writing onto the file
// An exception occurs if the file does
// not exist.
// The method returns an integer which
// is the file descriptor fd
const fd = fs.openSync("input.txt", "r+");
// This text will be written on file input.text
const text = "Welcome to GeeksforGeeks";
// Starting position in file
const position = 0;
// writeSync returns number of bytes written
// on file which is stores in this variable
const numberOfBytesWritten =
fs.writeSync(fd, text, position, 'utf8');
console.log('File written successfully using writeSync()');
console.log(`Text written on file: ${text},
starting from position: ${position}`);
console.log(`Number of Bytes written:
${numberOfBytesWritten}`);
使用以下命令运行 index.js 文件:
node index.js
控制台输出:
File written successfully using writeSync()
Text written on file: Welcome to GeeksforGeeks,starting from position: 0
Number of Bytes written: 24
示例:
index.js
// Importing fs module
const fs = require("fs");
// open file using openSync in writing mode
// The file is created if it does not exist
// or truncated if it exists
// The method returns an integer which is
// the file descriptor fd
const fd = fs.openSync("binaryFile", "w");
// Create a buffer which will be written
// onto the file
const buffer = new Buffer.from(
'GeeksforGeeks: A computer science portal for geeks');
// Starting position in file
const position = 0;
// writeSync returns number of bytes written
// on file which is stores in this variable
const numberOfBytesWritten =
fs.writeSync(fd, buffer, position, 50);
console.log('File written successfully using writeSync()');
console.log(`Buffer written on file: ${buffer},
starting from position: ${position}`);
console.log(`Number of Bytes written:
${numberOfBytesWritten}`);
使用以下命令运行 index.js 文件:
node index.js
控制台输出:
File written successfully using writeSync()
Buffer written on file: GeeksforGeeks: A computer science portal for geeks
starting from position: 0
Number of Bytes written: 50
参考:
- https://nodejs . org/API/fs . html # fs _ fs _ write sync _ FD _ string _ position _ encoding
- https://nodejs . org/API/fs . html # fs _ fs _ write sync _ FD _ buffer _ offset _ length _ position
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