Getting ASCII decimal numbers from a char array: why doesn't it work?

kanurys

Hello everyone. This is my first super-noob post here, so if I need to add more detail, please let me know.

I have the attached code which reads a log file, identifies the first character of each line and deletes the line if it is not a number (ASCII number).

The line which reads ascii_dec = char_array[0]; is causing the debug error "ArrayIndexOutOfBoundsException: 0". If I comment that line out it prints "50" which corresponds to ASCII character 2, as it is the first character of the last line in the log file. I get the same results if I change the byte data types to int.

Why doesn't it like the code in question and how should I change this to work correctly? I know, I suck at programming, so I'm sorry my implementation and technique may not be conventional. Thanks for the help -SK

String[] lines;

byte[] char_array;
byte ascii_dec;


void setup(){

  lines = loadStrings("log 11-23-2013 2-10pm.csv");

  for(int i = 0; i < lines.length; i++){

    //turn the line into individual char's
    char_array = lines[i].getBytes();
    //isolate the first char of the line
    ascii_dec = char_array[0];

    //test the first char to see if there is a number stored in the first entry of the line.
    //If not an ascii number, then delete the line from original array
    if(ascii_dec != 48 && ascii_dec != 49 && ascii_dec != 50 && ascii_dec != 51 && ascii_dec != 52 && ascii_dec != 53 && ascii_dec != 54 && ascii_dec != 55 && ascii_dec != 56 && ascii_dec != 57){
      lines[i] = "";
    }

  } 

  //saveStrings("log2.csv", lines); //implement this later

  //this is to test and make sure there is something in that element of char_array[]
  println(char_array[0]);
}


void draw(){}

Chrisir

I wouldn't recommend this line:

      lines[i] = "";

because you change the value of lines.length, so for-loop can not work properly.

I would instead recommend to copy the value into a new array

kanurys

Thanks, I will copy each line that begins with a number into a new array to save. Any idea about the original problem?

Chrisir

this test works

String[] lines = {
  "log 11-23-2013 2-10pm", 
  "12log 11-23-2013 2-10", 
  "6log 11-23-2013 2-10p", 
  "log 11-23-2013 2-10pm", 
  "12log 11-23-2013 2-10", 
  "6log 11-23-2013 2-10p"
};

byte[] char_array;
byte ascii_dec;

String []lines2 = new String [0];

void setup() {

  println ("length: "+lines.length);
  for (int i = 0; i < lines.length; i++) {

    //turn the line into individual char's
    char_array = lines[i].getBytes();
    //isolate the first char of the line
    ascii_dec = char_array[0];

    //test the first char to see if there is a number stored in the first entry of the line.
    //If not an ascii number, then delete the line from original array
    if (ascii_dec < 48 || ascii_dec > 57) {
      // lines[i] = "";
      lines2 = append(lines2, lines[i]);
      println(lines2);
    }
  } 

  //saveStrings("log2.csv", lines); //implement this later

  //this is to test and make sure there is something in that element of char_array[]
  println(char_array[0]);
}
// 

kanurys

Nice, I like your approach. I think the problem lays in how I import the file to lines[]. I just tried your modification with the code: lines = loadStrings("log 11-23-2013 2-10pm.csv"); and got the old problem. Perhaps there is a line with nothing in the csv file and that would make char_array[0] not exist?

If this is the case, how would I test for a line containing nothing, like: "" ?

Also, I think the operators in the if statement are reversed.

kanurys

Anybody have a way to deal with empty strings? This seems to be what's causing the original error, I just need a way to check for them and skip over them. Ideas?

Thanks, Chrisir, for your help to figure this out so far.

kanurys

Maybe I'll check the length of the char_array

PhiLho

String foo1 = "f";
println(foo1.length);
println(foo1.isEmpty());
String foo2 = "";
println(foo2.length);
println(foo2.isEmpty());

(untested)

koogs

one thing

if (ascii_dec < 48 || ascii_dec > 57) {

requires you to know what 48 and 57 are. it's not obvious. whereas

if (ascii_dec < '0' || ascii_dec > '9') {

helps make it clear that they are digits.

but perhaps even better is Character.isDigit()

http://www.tutorialspoint.com/java/character_isdigit.htm