Read string from binary file, different encodings

Question

I'm trying to read a binary file in Java (android) that was created by a C# program however i have stumbled in to a problem. C# by default encode string in binary file by UTF-7, Java uses UTF-8. This of course mean that the string don't get loaded in properly.

I was wonder how to read the string as UTF-7 instead of UTF-8. I also noticed that i got a similar problem with floats. Does C# and Java handle them differently and if so how do i read it correctly in Java.

Edit: I'm using the BinaryWriter class in the C# program and the DataInputStream class in java.

Erm, what are you asking? Some code or something to share with us in order to make your question a little more concrete? — Darin Dimitrov
– Darin Dimitrov, Commented Sep 9, 2012 at 20:36

SLaks · Accepted Answer · 2012-09-09 20:47:50Z

1

C# uses UTF-8 encoding unless otherwise specified.

EDIT The documentation here is incorrect.
Looking at the source, BinaryWriter writes the string length as a 7-bit encoded integer, using the following code:

    protected void Write7BitEncodedInt(int value) {
        // Write out an int 7 bits at a time.  The high bit of the byte, 
        // when on, tells reader to continue reading more bytes. 
        uint v = (uint) value;   // support negative numbers
        while (v >= 0x80) { 
            Write((byte) (v | 0x80));
            v >>= 7;
        }
        Write((byte)v); 
    }

You will need to port this code to Java in order to find out how many bytes to read.

edited Sep 9, 2012 at 20:47

answered Sep 9, 2012 at 20:35

SLaks

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4 Comments

Dragon Creature Over a year ago

According to the documentation it's UTF-7 msdn.microsoft.com/en-us/library/yzxa6408.aspx

SLaks Over a year ago

@Frozendragon: Wrong. It writes the lengthy as an integer encoded using UTF7, then writes the string using the writer's encoding. (UTF8 by default)

Dragon Creature Over a year ago

Does that not effect Javas ability to read it as a UTF-8 encoded string?

obataku Over a year ago

@SLaks see the final paragraph of the Description section of Wikipedia's article on UTF-7. "... however, ... instead of UTF-7, a little-endian variable-length quantity identical to LEB128 is used; and that in fact the count is a byte count and not a character count."

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