node.js中的fs.write方法使用说明

fs.write(fd, buffer, offset, length[, position], [callback(err, bytesWritten, buffer)])

fs.write(fd, data[, position[, encoding]], [callback(err, written, string)])

//fs.write(fd, buffer, offset, length[, position], [callback(err, bytesWritten, buffer)])
//执行结果：bytesWritten = 8 , buffer = <Buffer 00 00 00 01 00 00 00 00>
 
var fs = require('fs');
fs.open('content.txt', 'a', function(err,fd){
 if(err){
  throw err;
 }
 var data = '123123123 hello world';
 var buf = new Buffer(8);
 fs.write(fd, buf, 0, 8, 0, function(err, bytesWritten, buffer){
  if(err){
   throw err;
  }
  console.log(bytesWritten);
  console.log(buffer);
 
  fs.close(fd,function(err){
   if(err){
    throw err;
   }
   console.log('file closed');
  })
 })
})
 
//fs.write(fd, data[, position[, encoding]], [callback(err, written, string)])
//执行结果：written = 21 , string = <Buffer 31 32 33 31 32 33 31 32 33 20 68 65 6c 6c 6f 20 77 bf 72 6c 64>
var fs = require('fs');
fs.open('content.txt', 'a', function(err,fd){
 if(err){
  throw err;
 }
 var data = '123123123 hello world';
 fs.write(fd, data, 0 , 'utf-8', function(err, written, string){
  if(err){
   throw err;
  }
  console.log(written);
  console.log(string);
 
  fs.close(fd,function(err){
   if(err){
    throw err;
   }
   console.log('file closed');
  })
 })
})

// usage:
// fs.write(fd, buffer, offset, length[, position], callback);
// OR
// fs.write(fd, string[, position[, encoding]], callback);
fs.write = function(fd, buffer, offset, length, position, callback) {
  if (util.isBuffer(buffer)) {
    // if no position is passed then assume null
    if (util.isFunction(position)) {
      callback = position;
      position = null;
    }
    callback = maybeCallback(callback);
    var wrapper = function(err, written) {
      // Retain a reference to buffer so that it can't be GC'ed too soon.
      callback(err, written || 0, buffer);
    };
    return binding.writeBuffer(fd, buffer, offset, length, position, wrapper);
  }
  if (util.isString(buffer))
    buffer += '';
  if (!util.isFunction(position)) {
    if (util.isFunction(offset)) {
      position = offset;
      offset = null;
    } else {
      position = length;
    }
    length = 'utf8';
  }
  callback = maybeCallback(position);
  position = function(err, written) {
    // retain reference to string in case it's external
    callback(err, written || 0, buffer);
  };
  return binding.writeString(fd, buffer, offset, length, position);
};