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array to file (Read 580 times)
psycho_manson
array to file
Dec 27th, 2006, 11:26pm  
hi all,

i understand, how to read and write bytes into files, i.e.:

-----------------------------------------------------
byte[] out= {10,10,10};
saveBytes("test.dat", out);
byte in[] = loadBytes("test.dat");
-----------------------------------------------------

but, how do I get and array of numbers out onto my hard disk, i.e.:

int[] storedata = new int[10];
for (int i=1; i<10; i++){
storedata[i]=i;
}

byte[] = storedata[] //ahhh, something like this ..

thanks a lot!
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psycho_manson
Re: array to file
Reply #1 - Dec 28th, 2006, 11:32am  
aahhh, newbie me  ...

it works:

int[] test  = new int[12];
byte[] yes = new byte[255];


for (int a=1; a<255; a++){
 yes[a]  = byte(a);
 saveBytes("bla.dat", yes);
 }
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st33d
Re: array to file
Reply #2 - Dec 28th, 2006, 3:03pm  
Indeed n00b.

Integers comprise 4 bytes. So to save numbers beyond the value of 255 you will need to split before saving and combine after loading.

I can't find the old post where this was brought up in the first place though, so my functions are a bit russian spaceship (clunky and big, but do the job). They come from an old project. Perhaps someone will login and post tidier ones.
Code:

int byteToInt (byte [] source){
  int [] returnInt = new int[source.length];
  for (int i = 0; i < source.length; i++){
    returnInt[i] = int(source[i]);
  }
  return (returnInt[0] << 24)
    | (returnInt[1] << 16)
	| (returnInt[2] << 8)
	  | returnInt[3];
}

byte [] int4Bytes (int source){
  byte [] sendBack = new byte[4];
  sendBack[0]=byte((source&0xFF000000)>>24);
  sendBack[1]=byte((source&0x00FF0000)>>16);
  sendBack[2]=byte((source&0x0000FF00)>>8);
  sendBack[3]=byte((source&0x000000FF));
  return sendBack;
}
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psycho_manson
Re: array to file
Reply #3 - Dec 28th, 2006, 5:34pm  
merci beaucoup st33d,

finally i got around the job by writing a second array onto the hard drive which indicates the times i have passed 255 as an index for the first array so i add the missing bits back on when i read them - real Russian engineering!

don't forget coding is only fun for those who do it every day!

thanks!
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fjen
Re: array to file
Reply #4 - Dec 28th, 2006, 7:02pm  
just a thought, if you wanna get really fancy you could just write your (array as) object to disk. have a look at serialization.

F
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toxi
Re: array to file
Reply #5 - Dec 29th, 2006, 2:33am  
You can also make use of Java's built in DataOutputStream to handle automatic conversion from int's/float's/double's etc. into bytes and vice versa:

Code:
/**
 * Saves an int array as raw data (Big Endian order)
 * to a file in the sketch folder.
 *
 * @param fname file name
 * @param data int array
 */
void saveInts(String fname, int[] data) {
  try {
    DataOutputStream ds = new DataOutputStream(new FileOutputStream(sketchPath(fname)));
    for(int i=0; i<data.length; i++) ds.writeInt(data[i]);
    ds.flush();
    ds.close();
  } 
  catch(Exception e) {
    e.printStackTrace();
  }
}

/**
 * Loads an int array from a raw data file (Big Endian order)
 * in the sketch folder.
 *
 * @param fname file name
 * @return an int array
 */
int[] loadInts(String fname) {
  int[] data=null;
  try {
    FileInputStream fs = new FileInputStream(sketchPath(fname));
    DataInputStream ds = new DataInputStream(fs);
    data = new int[(int)(fs.getChannel().size()/4)];
    for (int i = 0; i < data.length; i++) data[i] = ds.readInt();
    ds.close();
    fs.close();
  } 
  catch(Exception e) {
    e.printStackTrace();
  }
  return data;
}
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