Java fast atoi using byte[]

Question

I'm working on an application that's supposed to read and process flat files. These files don't always use a consistent encoding for every field in a record, so it was decided that we should read/write bytes and avoid the necessary decoding/encoding of turning them into Strings.

However, a lot of these fields are simple integers, and I need to validate them (test that they are really integers and in a certain range). I need a function that receives a byte[] and turns that into an int. I'm assuming all the digits are plain ASCII.

I know I could do this by first turning the byte[] into a CharBuffer, decoding to ISO-8859-1 or UTF-8, and then calling Integer.parseInt() but that seems like a lot of overhead and performance is important.

So, basically what I need is a Java equivalent of atoi(). I would prefer an API function (including 3rd party APIs). Also, the function should report errors in some way.

As a side note, I'm having the same issue with fields representing date/time (these are more rare though). It would be great if someone could mention some fast C-like library for Java.

Have you seen thi [SO question](http://stackoverflow.com/questions/4950598/convert-byte-to-int) ? — Grooveek, Feb 01 '12 at 08:39
I would use a direct ByteBuffer to avoid the copy to a byte[] as well. — Peter Lawrey, Feb 01 '12 at 09:32

score 1 · Accepted Answer · answered Feb 01 '12 at 08:43

while i can not give you a ready java solution i want to point you onto interesting (c) code for you to read: the author of qmail has a small function to quickly parse unsigned longs from a byte array scan_ulong, you can find lots of incarnations of that function all over the web:

unsigned int scan_ulong(register const char *s,register unsigned long *u)
{
  register unsigned int pos = 0;
  register unsigned long result = 0;
  register unsigned long c;
  while ((c = (unsigned long) (unsigned char) (s[pos] - '0')) < 10) {
    result = result * 10 + c;
    ++pos;
  }
  *u = result;
  return pos;
}

(taken from here: https://github.com/jordansissel/djbdnsplus/blob/master/scan_ulong.c )

that code should translate pretty smoothly to java.

score 1 · Answer 2 · answered Feb 01 '12 at 08:51

The atoi function from the C library is an incredibly dull piece of code: you can translate it to Java in five minutes or less. If you must avoid writing your own, you could use the String(byte\[\] buf, int offset,int length) constructor to make Java string bypassing CharBuffer, and parse it to complete the conversion.

Java fast atoi using byte[]

2 Answers2