javascript - 为什么缓冲区复制会打印一些垃圾值？

Question

我是 Node.js 新手，

我正在阅读 Node.js 缓冲区。

我偶然发现了 buffer.copy 方法。

编写了如下代码，

var bufferOne = new Buffer("This is China");
var bufferTwo = new Buffer(20),
   startTarget = 0,
   sourceStart = 8,
   sourceEnd = 0;
var bufferLength = bufferOne.length;
sourceEnd = bufferLength;
console.log("Buffer length "+bufferLength);
bufferOne.copy(bufferTwo,startTarget,sourceStart,sourceEnd);

console.log("Buffer1 "+bufferOne.toString());   
console.log("Buffer2 "+bufferTwo.toString());

输出如下，

Buffer length 13
Buffer1 This is China
Buffer2 China

但有时它也会在“China”之后打印垃圾输出，如下，

Buffer length 13
Buffer1 This is China
Buffer2 China���*�

有时，

Buffer length 13
Buffer1 This is China
Buffer2 China���

有人可以告诉我发生了什么事吗？

Answer 1

bufferTwo 的长度是 20，但您只复制 13 个字节。其余 7 个字节包含半随机数据。

记录here :

Passing a number as the first argument to Buffer() (e.g. new Buffer(10)), allocates a new Buffer object of the specified size. The memory allocated for such Buffer instances is not initialized and can contain sensitive data.