Ctypes How to set OSType which expects characters but is defined as unsigned int (OSX)

Question

So with CTypes Im tryng to convert this code below. It uses OSType, OSType is dfined as

FourCharCode = ctypes.c_uint32
OSType = FourCharCode
QTPropertyClass = OSType

We see here it is an usngiend character. But We see in snippet below they defined it as

const OSType    kFinderSig = 'MACS';

So in ctypes, setting a variable to 'MACS' would not e c_uint32 type but it will be char no?

Please advise.

Thanks

https://stackoverflow.com/a/8895297/1828637

OSStatus    SendFinderSyncEvent( const FSRef* inObjectRef )
{
    AppleEvent  theEvent = { typeNull, NULL };
    AppleEvent  replyEvent = { typeNull, NULL };
    AliasHandle itemAlias = NULL;
    const OSType    kFinderSig = 'MACS';

    OSStatus    err = FSNewAliasMinimal( inObjectRef, &itemAlias );
    if (err == noErr)
    {
        err = AEBuildAppleEvent( kAEFinderSuite, kAESync, typeApplSignature,
            &kFinderSig, sizeof(OSType), kAutoGenerateReturnID,
            kAnyTransactionID, &theEvent, NULL, "'----':alis(@@)", itemAlias );

        if (err == noErr)
        {
            err = AESendMessage( &theEvent, &replyEvent, kAENoReply,
                kAEDefaultTimeout );

            AEDisposeDesc( &replyEvent );
            AEDisposeDesc( &theEvent );
        }

        DisposeHandle( (Handle)itemAlias );
    }

    return err;
}

score 2 · Accepted Answer · edited May 23 '17 at 12:20

2

const OSType    kFinderSig = 'MACS';

'MACS' is a character constant, not a string! This code is using a (questionable) GCC extension for multi-character character constants.

You can reproduce the results in Python using the (builtin) struct module:

import struct
kFinderSig = struct.unpack(">L", "MACS")[0]

Alternatively, just hard-code the value as 0x4d414353 and leave a comment that it represents "MACS".

edited May 23 '17 at 12:20

Community

1
1

answered Jan 13 '15 at 02:14

Thank you a thousand times!! This was driving me nuts!! A special thank you for two solutions in one! I love learning from seeing different ways doing the same thing, that helps a ton!! – Noitidart Jan 13 '15 at 04:38
1

In Python 3 you can also use `kFinderSig = int.from_bytes(b'MACS', 'big')`. ctypes data types aren't as convenient here due to the big-endian requirement: `kFinderSig = c_uint32.__ctype_be__.from_buffer_copy(b'MACS')`. – Eryk Sun Jan 13 '15 at 15:22

Ctypes How to set OSType which expects characters but is defined as unsigned int (OSX)

1 Answers1