})
})
//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’);
})
})
})
源码：
// 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);
};
