Re: Reading a C struct in java

RedGrittyBrick <RedGrittyBrick@SpamWeary.invalid>
Wed, 30 Sep 2009 13:40:37 +0100
Arne Vajh??j wrote:

RedGrittyBrick wrote:

Mark wrote:

On Tue, 29 Sep 2009 11:33:29 +0200, Lothar Kimmeringer
<> wrote:

Mark wrote:

I am writing an app in java which reads data from a socket from a C
language program. The data is encoded as a C struct of char arrays
something like this;

typedef struct {
    char type[1];
    char length[6];
    char acknowledge[1];
    char duplicate[1];
} type_t;

How can I decode a structure like this in Java without using JNI (a


The data arrives to my code in already in a byte array.

I guess I want to know if there is an easy way to map the C structure
to a java class or whether I will have to dissect the byte array
completely manually.

Someone please put me out of my misery, I'm missing something obvious,
why can't Mark do something like


import java.util.Arrays;

public class DecodeStruct {
    public static void main(String[] args) {

        char[] struct = {'t','0','0','0','0','2','1','N','A'};

        Foo foo = new Foo(struct);

        System.out.println("length is " + foo.getLengthAsString());

class Foo {
    private char type;
    private char[] length;
    private char duplicate;
    private char acknowledge;

    Foo (char[] struct) {
        type = struct[0];
        length = Arrays.copyOfRange(struct, 1, 7);
        duplicate = struct[7];
        acknowledge = struct[8];

    public String getLengthAsString() {
        return new String(length);

length is 000021

Does it "map the C structure to a java class" ?

Not really I suppose, at least, not dynamically. Nor is it different
from the "dissect the byte array completely manually" that Mark wished
to avoid.

However it is the first thing I'd think of in order to instantiate a
Java class from a byte array whose contents originated from a C struct.
It just doesn't seem that bad to me.


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