Re: Reading a C struct in java

Patricia Shanahan <>
Tue, 29 Sep 2009 08:18:48 -0700
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

I expect this to map most directly to four byte[] arrays in Java.

Here's an idea for a method that might be useful:


public byte[][] getRaw(InputStream in, int... sizes) throws IOException{
   byte[][] result = new byte[sizes.length][];
   for(int i=0; i<sizes.length; i++){
     result[i] = new byte[sizes[i]];[i]);
   return result;

If I've got this right, the result of calling:

getRaw(in, 1, 6, 1, 1)

should be a four element array of byte[], with each element containing
the raw data from one of the fields. That could be used, for example, as
a constructor parameter for a class that represents type_t in Java, with
each fields converted to a more useful type. For example, if duplicate
is logically a boolean, the class would have a boolean field,
initialized according to how the C char represents booleans.


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