Node.js | Buffer.readUInt32LE() 方法

Buffer.readUInt32LE() 方法是 Buffer 模块中 Buffer 类的内置应用程序编程接口，用于以小端格式从指定偏移量的已分配缓冲区中读取 32 位值。

句法：

Buffer.readUInt32LE( offset )

参数：此方法接受单个参数偏移量，它指定在读取之前要跳过的字节数，或者只是表示缓冲区中的索引。 offset 的值是0 <= offset <= Buffer.length – 4 。它的默认值为 0。

返回值：此方法以小端格式返回从缓冲区读取的整数值。

下面的示例说明了 Node.js 中 Buffer.readUInt32LE() 方法的使用：

示例 1：

// Node program to demonstrate the  
// Buffer.readUInt32LE() Method
   
// Allocating buffer from array
const buf = Buffer.from([0x21, 0x09, 0x19,
             0x98, 0x16, 0x09, 0x19, 0x96]);
  
// Printing allocated buffer
console.log(buf);
   
// Reading 32bits data from the buffer
// and printing it as a string
console.log(buf.readUInt32LE(0).toString(16));
console.log(buf.readUInt32LE(1).toString(16));
console.log(buf.readUInt32LE(2).toString(16));
console.log(buf.readUInt32LE(3).toString(16));
console.log(buf.readUInt32LE(4).toString(16));

输出：

98190921
16981909
9169819
19091698
96190916

示例 2：

// Node program to demonstrate the  
// Buffer.readUInt32LE() Method
   
// Allocating buffer from array
const buf = Buffer.from([0x21, 0x09, 0x19, 0x98,
                     0x34, 0xae, 0xe8, 0xff]);
  
// Printing allocated buffer
console.log(buf);
   
// Reading 16bits data from the buffer
// and printing it as a string
console.log(buf.readUInt32LE(0).toString(16));
console.log(buf.readUInt32BE(0).toString(16));
console.log(buf.readUInt32LE(1).toString(16));
console.log(buf.readUInt32BE(1).toString(16));
console.log(buf.readUInt32LE(2).toString(16));
console.log(buf.readUInt32BE(2).toString(16));
console.log(buf.readUInt32LE(3).toString(16));
console.log(buf.readUInt32BE(3).toString(16));
console.log(buf.readUInt32LE(4).toString(16));
console.log(buf.readUInt32BE(4).toString(16));

输出：

98190921
21091998
34981909
9199834
ae349819
199834ae
e8ae3498
9834aee8
ffe8ae34
34aee8ff

示例 3：

// Node program to demonstrate the  
// Buffer.readUInt32LE() Method
   
// Allocating buffer from array
const buf = Buffer.from([0x21, 0x09, 0x19, 0x98]);
  
// Printing allocated buffer
console.log(buf);
   
// Reading 16bits data from the buffer
// and printing it as a string
console.log(buf.readUInt32LE(0).toString(16));
   
// Wrong index is provoded to produce error
console.log(buf.readUInt32LE(1).toString(16));

输出：

98190921
internal/buffer.js:49
  throw new ERR_OUT_OF_RANGE(type || 'offset',
  ^
RangeError [ERR_OUT_OF_RANGE]: The value of "offset" is out of range. 
It must be >= 0 and <= 0. Received 1
    at boundsError (internal/buffer.js:49:9)
    at Buffer.readUInt32LE (internal/buffer.js:105:5)
    at Object. (C:\nodejs\buf_readuint32le_2.js:10:17)
    . . .

注意：以上程序将使用node index.js命令编译运行。

参考： https://nodejs.org/api/buffer.html#buffer_buf_readuint32le_offset