Excel VBA: "Run-time error '49': Bad DLL calling convention" calling C++ dll

Question

I am attempting to call a C++ DLL from Excel-VBA.

I know the DLL function is being executed as I inserted fputs() logging calls to track execution and the stamps are showing up in my log file. The problem is, whenever the DLL function returns, I get Error 49.

Here is the declaration in VBA:

Private Declare Function InitMCR Lib "MCRBoilerplate.dll" Alias "?initMCR@@YGXXZ" ()

and here is the declaration in C++

__declspec(dllexport) void __stdcall initMCR() { ... }

Why am I getting this Error 49 behavior, even though the DLL calls appear to be working?

OK, I seem to have misinterpreted your 1st version too early not being a valid question. Now I see, you wanted to provide another Q&A by giving the solution. I'd recommend you put your solution part as an answer to the question. You can do so here, it's valid and encouraged. — πάντα ῥεῖ
– πάντα ῥεῖ, Commented Jul 4, 2014 at 18:00
@wgrant /OT Note: You don't need to click save to get intermediate versions of your edits backed up here (SO backs up your drafts while you're editing after a certain time). As soon you click save, you're publishing your stuff, and you may receive downvotes and critique about your actually unfinished stuff. Sorry for the initial down/close votes, you're welcome in general. Put your solution as an answer as suggested, and I'd even upvote both of it. — πάντα ῥεῖ
– πάντα ῥεῖ, Commented Jul 4, 2014 at 18:11
@david-heffernan Nice action, but my initial intention was to get the OP learning s.th. about how the site works. You're right, I should have been clarifying using another comment (did so now). — πάντα ῥεῖ
– πάντα ῥεῖ, Commented Jul 4, 2014 at 20:02
Thanks for the insight everyone. I had intended to provide the answer immediately as @Niall and πάντα ῥεῖ suggested but since I had less than 10 rep, SO made me wait 24 hours before posting an answer. You guys beat me to the punch :) — wgrant
– wgrant, Commented Jul 7, 2014 at 18:44

5 revs, 2 users 94% · Accepted Answer · 2014-07-04 19:57:58Z

2

In VBA, functions that return void need to be declared as Sub instead of Function

So the declaration in VBA should be:

Private Declare Sub InitMCR Lib "MCRBoilerplate.dll" Alias "?initMCR@@YGXXZ" ()

See MSDN page on VBA Declare statement

edited Jul 4, 2014 at 19:57

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5 revs, 2 users 94%
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Community · Accepted Answer · 2017-05-23 11:53:12Z

A quick point: your problem might not be a parameter mismatch in your external function, or in the declaration that imports it - there's a known compiler glitch in VBA that raises error 49.

'Stacker pstraton's answer to 'Excel - Runtime Error 49: Bad DLL calling convention'

You're not completely blameless - you probably have a parameter mismatch with a returned type that should work (Long populating an Int, Variants populating just about anything) in the calling function - but I have never heard of anyone banishing a persistent Runtime Error 49 by better coding. You just recompile, or export and reimport the modules.

The worst of it is that a genuine Forty-Niner is far harder to debug than it needs to be: the statement that triggers the error message usually isn't a call to the misdeclared external function. If you're lucky, it's the 'Exit Sub' of the caller; and some of the time it's something further up the stack that you can trace back to the bad call; but, sometimes, it isn't obvious at all and there's no deterministic debugging strategy at all.

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