how to copy a file

cocos2d-x JavaScript
#1

I use the code to read data from file and write the data to another place.

var v0=69632;//file size
var vvv= cc.FileUtils.getInstance().getFileData( “myfile.data”, “r”,v0);
//jsb to write vvv to a file in writable path

but it reports

Cocos2d: Get data from file(myfile.data) failed!

the size of file ‘myfile.data’ in writable path is only 12,288 bytes rather than 69,632 bytes