evm_doc/zh-cn/evm_class_buffer.md at master · scriptiot/evm_doc

平台支持

API	OS
buf.compare	Linux，RT-Thread, Zephyr
buf.copy	Linux，RT-Thread, Zephyr
buf.equals	Linux，RT-Thread, Zephyr
buf.fill	Linux，RT-Thread, Zephyr
buf.from	Linux，RT-Thread, Zephyr
buf.slice	Linux，RT-Thread, Zephyr
buf.toString	Linux，RT-Thread, Zephyr
buf.write	Linux，RT-Thread, Zephyr
buf.writeUInt8	Linux，RT-Thread, Zephyr
buf.writeUInt16LE	Linux，RT-Thread, Zephyr
buf.writeUInt32LE	Linux，RT-Thread, Zephyr
buf.readInt8	Linux，RT-Thread, Zephyr
buf.readUInt8	Linux，RT-Thread, Zephyr
buf.readUInt16LE	Linux，RT-Thread, Zephyr

Buffer

new Buffer(size)

size {integer} buffer大小.

var Buffer = require('buffer');

var buffer = new Buffer(5);

new Buffer(buffer)

buffer {Buffer} 缓存数组.

var Buffer = require('buffer');

var buffer1 = new Buffer(5);
var buffer2 = new Buffer(buffer1);

new Buffer(str[, encoding])

str {string} 字符串.
encoding {string} 编码格式.

var Buffer = require('buffer');

var buffer = new Buffer(String.fromCharCode(65));

// prints: 1
console.log(buffer);

var buffer = new Buffer(String.fromCharCode(128));

// prints: 2
console.log(buffer);

var buffer = new Buffer(String.fromCharCode(2048));

// prints: 3
console.log(buffer);

var buffer = new Buffer('4142', 'hex');

// prints: AB
console.log(buffer);

new Buffer(array)

array {Array} 数字数组.

var buffer = new Buffer([65, 256 + 65, 65 - 256, 65.1]);

// prints: AAAA
console.log(buffer);

Buffer.byteLength(str, encoding)

str {string} 字符串.
encoding {string} 字符串编码.
Returns: {integer} 返回字符串的字节缓存长度.

var Buffer = require('buffer');

// prints: 1
console.log(Buffer.byteLength(String.fromCharCode(65)));

// prints: 2
console.log(Buffer.byteLength(String.fromCharCode(128)));

// prints: 3
console.log(Buffer.byteLength(String.fromCharCode(2048)));

// prints: 2
console.log(Buffer.byteLength('4142', 'hex'));

Buffer.concat(list)

list {Array} buffer对象列表.

var Buffer = require('buffer');

var buffer = Buffer.concat([ new Buffer('He'),
                             new Buffer('llo'),
                             new Buffer(' wo'),
                             new Buffer('rld') ])

// prints: Hello world
console.log(buffer);

Buffer.from(array)

array {Array} 数字数组.
Returns: {Buffer} 返回包含数组元素的缓存对象。

var Buffer = require('buffer');

var source = new Buffer[65, 66, 67];
var buffer = Buffer.from(source);

//prints: ABC
console.log(buffer.toString());

Buffer.from(string[,encoding])

str {String} 字符串.
encoding {String} 编码格式.
Returns: {Buffer} 返回包含字符串元素的缓存对象。

var Buffer = require('buffer');

var buffer = Buffer.from('4142','hex');

//prints: AB
console.log(buffer.toString());

Buffer.from(buffer)

buffer {Buffer} 缓存对象.
Returns: {Buffer} 返回buffer的拷贝对象。

var Buffer = require('buffer');

var source = new Buffer(12);
var buffer = Buffer.from(source);

Buffer.from(arrayBuffer[, byteOffset[, length]])

arrayBuffer {ArrayBuffer} Arraybuffer 或者 TypedArray。
byteOffset {Number} 索引偏移位置. 默认: 0.
length {Number} 数组长度. 默认: arrayBuffer.length - byteOffset.
Returns: {Buffer} 返回包含arrayBuffer的指定范围元素的缓存对象。

var source = new ArrayBuffer(12);
var buffer = Buffer.from(source, 0, 2);

//prints: 2
console.log(buffer.length);
var typed_source = new Uint8Array([65,66]);
var arr_buff = Buffer.from(typed_source1.buffer, 0, 2);

//prints: AB
console.log(buff.toString('utf-8'));

Buffer.isBuffer(obj)

obj {Object} 对象。
Returns: {boolean} 返回bool值。

var Buffer = require('buffer');

// prints: true
console.log(Buffer.isBuffer(new Buffer(1)));

// prints: false
console.log(Buffer.isBuffer('str'));

buf.length

缓存对象容量长度。

var Buffer = require('buffer');

var buffer = new Buffer([0xc8, 0x80]);

// prints: 2
console.log(buffer.length);

var str = buffer.toString();

// prints: 1
console.log(str.length);

buf.compare(otherBuffer)

otherBuffer {Buffer} 待比较的缓存对象.
Returns: {integer}

这个函数用来比较两个缓存对象内容是否相同。如果两个对象相同，返回0；如果当前对象缓存长度大于待比较的缓存对象的长度，返回1；小于则返回-1.

var Buffer = require('buffer');

var buffer = new Buffer([0xc8, 0x80]);

// prints: 2
console.log(buffer.length);

var str = buffer.toString();

// prints: 1
console.log(str.length);

buf.copy(targetBuffer[, targetStart[, sourceStart[, sourceEnd]]])

targetBuffer {Buffer} 缓存对象.
targetStart {Integer} 默认值：0
sourceEnd {integer} 默认值: buf.length
Returns: {integer} 拷贝的字节长度.

var Buffer = require('buffer');

var buffer1 = new Buffer('Hello XY world!');
var buffer2 = new Buffer('<JS>');

buffer2.copy(buffer1, 6, 1, 3);

// prints: Hello JS world!
console.log(buffer1);

buf.equals(otherBuffer)

otherBuffer {Buffer} 待比较缓存对象.
Returns: {boolean}

var Buffer = require('buffer');

var buffer1 = new Buffer('AB');
var buffer2 = new Buffer('4142', 'hex');
var buffer3 = new Buffer('A');

// prints: true
console.log(buffer1.equals(buffer2));

// prints: false
console.log(buffer1.equals(buffer3));

buf.fill(value)

value {integer} 待填充的值.
Returns: {Buffer} 原始缓存对象.

var Buffer = require('buffer');

var buffer = new Buffer('Hello');

buffer.fill(65);

// prints: AAAAA
console.log(buffer);

buffer.fill(66 - 256);

// prints: BBBBB
console.log(buffer);

buf.slice([start[, end]])

start {integer} 默认值: 0
end {integer} 默认值: buf.length
Returns: {Buffer} 新创建的缓存对象.

var Buffer = require('buffer');

var buffer = new Buffer('This is JavaScript!!!');

// prints: JavaScript
console.log(buffer.slice(8, 18));

buf.toString([start[, end]])

start {integer} 默认值: 0
end {integer} 默认值: buf.length
Returns: {string}。

var Buffer = require('buffer');

var buffer = new Buffer('DEFG');

// prints: EF
console.log(buffer.toString(1, 3));

// prints: 44454647
console.log(buffer.toString('hex'));

buf.write(string[, offset[, length]])

string {string} 写入缓存对象的数据.
offset {integer} 写入数据的起始地址. 默认值: 0
length {integer} 写入数据的长度. 默认值: buffer.length - offset.
Returns: {integer} 返回写入数据的总长度.

var Buffer = require('buffer');

var buffer = new Buffer('......');
buffer.write('AB');
buffer.write('XY', 3);

// prints: AB.XY.
console.log(buffer);

var buffer = new Buffer('......');
buffer.write('ABCDEF', 1, 3);

// prints: .ABC..
console.log(buffer);

buf.writeUInt8(value, offset[, noAssert])

string {string} 写入缓存对象的数据.
offset {integer} 写入数据的起始地址. 默认值: 0
length {integer} 写入数据的长度. 默认值: buffer.length - offset.
Returns: {integer} 返回写入数据的总长度.

var Buffer = require('buffer');

var buffer = new Buffer('......');
buffer.write('AB');
buffer.write('XY', 3);

// prints: AB.XY.
console.log(buffer);

var buffer = new Buffer('......');
buffer.write('ABCDEF', 1, 3);

// prints: .ABC..
console.log(buffer);

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