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From: John McCabe <john@nospam.assen.demon.co.uk>
Newsgroups: comp.lang.ada
Subject: Re: This MIDI stuff,
 would someone be interested in reviewing my code?
Date: Wed, 10 Mar 2010 12:29:00 +0000
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Date: 2010-03-10T12:29:00+00:00
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On Wed, 10 Mar 2010 06:12:11 -0500, Stephen Leake
<stephen_leake@stephe-leake.org> wrote:

>John McCabe <john@nospam.assen.demon.co.uk> writes:
>
>>>I had them declared as aliased. With just 'access on it the compiler
>>>said "blah blah blah can't do it because it's not global" (or
>>>something like that). I'll check again, but that was the gist of it.
>>
>> mididevs.adb:56:49: non-local pointer cannot point to local object
>>
>> Note - this is an updated version so the lines aren't the same number!
>>
>> That's with something like:
>>
>> procedure MidiDevs is
>>    Midi_In_Caps : aliased Win32.Mmsystem.MIDIINCAPS;
>
>This object is declared in a procedure, and is therefore allocated on
>the stack.

That's right.

>> begin
>>    <blah>
>>    res := Win32.Mmsystem.midiInGetDevCaps(Device_ID,
>>                                           Midi_In_Caps'Access,
>
>This function takes a parameter of a global access type.
>
>So in theory, the function could store a copy of the pointer, and then
>use it after MidiDevs has returned, and the actual object disappeared. 
>
>That's why this is illegal.

Exactly.

>However, if MidiDevs is really your main procedure, then Midi_In_Caps
>will never disappear, and 'Unchecked_Access is safe.

Fair point. Thanks.