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    <p>you have several options.</p> <p>since it looks like you want a contiguous glob of data in the NSData representation...</p> <p>you'll want to create a packed struct, and pass the data to the NSData call as a predefined endianness (so both ends know how to unarchive the data glob).</p> <pre><code>/* pack this struct's ivars and and enable -Wreorder to sanity check that the compiler does not reorder members -- i see no reason for the compiler to do this since the fields are equal size/type */ struct t_midi_message { UInt8 message_type; /* 0-15 */ UInt8 channel; /* 0-15 */ UInt8 data1; /* 0-127 */ UInt8 data2; /* 0-127 */ }; union t_midi_message_archive { /* members - as a union for easy endian swapping */ SInt32 glob; t_midi_message message; enum { ValidateSize = 1 / (4 == sizeof(t_midi_message)) }; /* nothing unusual here, although you may want a ctor which takes NSData as an argument */ t_midi_message_archive(); t_midi_message_archive(const t_midi_message&amp;); t_midi_message_archive(const t_midi_message_archive&amp;); t_midi_message_archive&amp; operator=(const t_midi_message_archive&amp;); /* swap routines -- just pass @member glob to the system's endian routines */ void swapToNativeEndianFromTransferEndian(); void swapToTransferEndianFromNativeEndian(); }; void a(const t_midi_message_archive&amp; msg) { t_midi_message_archive copy(msg); copy.swapToTransferEndianFromNativeEndian(); NSData * packedData([NSData dataWithBytes:&amp;copy.glob length:sizeof(copy.glob)]); assert(packedData); t_midi_message_archive recovered; [packedData getBytes:&amp;recovered.glob]; recovered.swapToNativeEndianFromTransferEndian(); /* recovered may now be used safely */ } </code></pre>
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    1. POPacking ints to bytes (NSData)
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    1. COSorry, maybe I wasn't clear: I don't need a big glob of data in the NSData. I'd like to get my 3 bytes worth of info into an NSData any way possible. I'm not worried about the messages being super-small inside the iOS, but I'd like the bytes underlying the NSData to be 3.
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      1. USDan Rosenstark
    2. COi count 4 - compilation will bail if: enum { ValidateSize = 1 / (4 == sizeof(t_midi_message)) }; is false. EDIT: ok you could reduce it to 3 - which seems like an unnecessary micro-optimization.
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    3. COif you really want 3 instead of 4, you'd just use bitfields in t_midi_message.
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