C structure in JAVA equavilent


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C structure in JAVA equavilent

Postby oo » Wed, 09 Jul 2003 17:29:23 GMT

I am doing this in c/c++:

struct MY_REC
   short nLen;
   char  szName[9];
} myRec;

myRec.nLen = 9;
strcpy(myRec.Name, "Superman");

write(&myRec, sizeof MY_REC);

The write() function will take the address of myRec and write the whole
structure to file. The binary value of nLen will be wriiten to file.

How can I achieve this in Java?

Re: C structure in JAVA equavilent

Postby Joseph Millar » Wed, 09 Jul 2003 19:25:21 GMT

See the java.io.Serializable interface and its use in the API docs.

Also, there is nothing to prevent you having a read() and write()
method as part of your class that know now to dump/get saved state


Re: C structure in JAVA equavilent

Postby Steve Horsley » Wed, 09 Jul 2003 19:32:21 GMT

I asume you want to write a compatible file in java?

First you need to specify the exact file format:
* What characterset / text encoding scheme does the file use?
  Is is ASCII, CP2125, 8859-1 etc.
* What encoding does the short use?
  How many bytes, and in what order? Is it signed?
* What happens if the name is <> than 8 characters?

Use shift-and-mask to make up the bytes for the short.
Use String.getBytes(String encoding) to get the string bytes
Don't forget to write the trailing zero byte.

    byte[] stringBytes = name.getBytes("ISO8859-1");
    byte msb = (byte) ((nLen >> 8) & 0xFF);
    byte lsb = (byte) (nLen & 0xfF);
    myOutputStream.write((byte) 0);


Re: C structure in JAVA equavilent

Postby Jon A. Cruz » Thu, 10 Jul 2003 01:09:28 GMT

Chances are the C code is broken and you don't even know it.

That's a *very* bad thing to do. When you write C/C++ code like that, 
you get broken results. Running on different types of computers will 
break it. Compiling with different switches will break it. Compiling 
with different compilers might break it. Even using all the exact same 
settings, but a newer version of the same compiler from the same vendor 
might break it.

*Never* read and write structs directly.

Write clean, proper C code. The write the same code in Java. It can end
up almost identical.

Follow the advice from Steve Horsley in doing this.

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