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POSending a Java UUID to C++ as bytes and back over TCP
 

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    <p>I'm trying to send a Java UUID to C++, where it will be used as a GUID, then send it back and see it as a UUID, and I'm hoping to send it across as just 16 bytes.</p> <p>Any suggestions on an easy way to do this?</p> <p>I've got a complicated way of doing it, sending from Java to C++, where I ask the UUID for its least and most significant bits, write this into a ByteBuffer, and then read it out as bytes.</p> <p>Here is my silly-complicated way of getting 2 longs out of a UUID, sending them to C++:</p> <p>Java</p> <pre><code>public static byte[] asByteArray(UUID uuid) { long msb = uuid.getMostSignificantBits(); long lsb = uuid.getLeastSignificantBits(); byte[] buffer = new byte[16]; for (int i = 0; i &lt; 8; i++) { buffer[i] = (byte) (msb &gt;&gt;&gt; 8 * (7 - i)); } for (int i = 8; i &lt; 16; i++) { buffer[i] = (byte) (lsb &gt;&gt;&gt; 8 * (7 - i)); } return buffer; } byte[] bytesOriginal = asByteArray(uuid); byte[] bytes = new byte[16]; // Reverse the first 4 bytes bytes[0] = bytesOriginal[3]; bytes[1] = bytesOriginal[2]; bytes[2] = bytesOriginal[1]; bytes[3] = bytesOriginal[0]; // Reverse 6th and 7th bytes[4] = bytesOriginal[5]; bytes[5] = bytesOriginal[4]; // Reverse 8th and 9th bytes[6] = bytesOriginal[7]; bytes[7] = bytesOriginal[6]; // Copy the rest straight up for ( int i = 8; i &lt; 16; i++ ) { bytes[i] = bytesOriginal[i]; } // Use a ByteBuffer to switch our ENDIAN-ness java.nio.ByteBuffer buffer = java.nio.ByteBuffer.allocate(16); buffer.order(java.nio.ByteOrder.BIG_ENDIAN); buffer.put(bytes); buffer.order(java.nio.ByteOrder.LITTLE_ENDIAN); buffer.position(0); UUIDComponents x = new UUIDComponents(); x.id1 = buffer.getLong(); x.id2 = buffer.getLong(); </code></pre> <p>C++</p> <pre><code> google::protobuf::int64 id1 = id.id1(); google::protobuf::int64 id2 = id.id2(); char* pGuid = (char*) &amp;guid; char* pGuidLast8Bytes = pGuid + 8; memcpy(pGuid, &amp;id1, 8); memcpy(pGuidLast8Bytes, &amp;id2, 8); </code></pre> <p>This works, but seems way too complex, and I can't yet get it working in the other direction.</p> <p>(I'm using google protocol buffers to send the two longs back and forth)</p> <ul> <li>Alex</li> </ul>
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