C++ why use TLB files over the actual DLL? - c++

I have some legacy C++ code.
I have DLL Bob.
I also have program Jane.
Program Jane imports Bob through his TLB file.
#import 'Bob.tlb'
Why does Jane use Bob like that?
Why doesn't Jane use Bob like this?
#import 'Bob.dll'
I have the source code for both sides.
Thanks for any help or pointers!

#importing a dll is equivalent to importing a tlb only when the dll contains the type library as the resource of ITypeLib type, as dictated by LoadTypeLib API call.
This is not always the case:
the dll doesn't have to contain the tlb as the resource
you might want to use a managed dll via COM interop: the dll doesn't contain the tlb and you have to generate it using tlbexp tool
there are probably other scenarios

TLB is type definition, which also can includes in DLL.
If you directly use #import *.tlb or #import *.dll, the MIDL Compiler would generate .tlh and .thi which used in following compiling steps.
It's not a good choice to directly #import.
If you #import the same .tlb in different cpp in same project, would introduce duplication .tlh & .tli files generated.

Related

How to use Superpowered lib in Swift project

I want to make an app in Swift that simply record via the mic of the iPhone and then play the sound recorded.
For that, I'd like to use the lib Superpowered that is a static library with header files.
For that, I tried to drag and drop the .a and headers files in my project (Xcode create for me a bridging header file), add the .a in "Linked Frameworks and Libraries" in Xcode > Target > General (and so in Xcode > Target > Build phases > "Link Binary With Libraries" too) and index the .h files path in Xcode > Target > Build Settings > Search Paths > Library Search Paths.
But with that I have the error "ld: symbol(s) not found for architecture arm64"
Exactly the same as here XCode: Undefined symbols for architecture arm64 error and I tried all the solutions that I found on the web for that, still no way to compile.
SO !
Superpowered gives us a sample app to show how to mix Objective-C++ and use their lib within a Swift project (Here's a link to the git if you want https://github.com/superpoweredSDK/Low-Latency-Android-Audio-iOS-Audio-Engine).
Here is some screenshots of the sample project with what I understand and what I don't :
The Bridging-Header-File with the prototypes of the methods of the lib that I want to use within my Swift code (I don't like this but if it's the only way...).
The viewController file where the code in Swift is, and where I can create a Superpowered object thank's to the Bridging-Header-File, and call the methods that I've put in it.
And wtf I don't even understand why this Objective-C++ file is here and what it contains. It comes out from nowhere, not even their lib files.
So with this sample project in mind, I've created my own project, here is some screenshots :
The same Bridging-Header-File that in the sample project except that I include SuperpoweredIOSAudioIO.h so I can use SuperpoweredIOSAudioIODelegate.
My viewController file where the code in Swift is, and where I can create a Superpowered object thank's to the Bridging-Header-File, and call the methods that I've put in it.
Until here, it's great, except that I can't for exemple create a SuperpoweredRecorder object. If I try to include the SuperpoweredRecorder.h file in my Bridging-Header-File I have these errors :
So I saw that it is because SuperpoweredRecorder.h includes some .cpp files and I have to create a wrapper for cpp (a little bit like I did with the bridging header, no ?) but that includes a .h and a .mm file and I don't know what I have to put in that .mm file (the code of SuperpoweredRecorder.cpp ? But I don't have access to it)
So yes, I'm a little bit confused with all that stuff, can you help me to understand how can I use all the Superpowered lib in my Swift project please ?
As I said in comment to #OmniProg, I had a little conversation with the CTO of Superpowered that helped me a lot to find the solution below.
So, as Swift cannot interact directly with C++ but can with Objective-C, I had to create objects in Objective-C++ (.mm file, a mix between C++ and Objective-C) that wrap C++ classes of the lib Superpowered.
Here is an example with the SuperpoweredRecorder object from the lib :
Here I create a .h file where I prototype my wrapper with the name SuperpoweredRecorderWrapped, and I also prototype in it all the methods of the SuperpoweredRecorder of the lib that I want to use.
Then I create a new .m file that I rename .mm and I implement SuperpoweredRecorderWrapped on it.
I import both SuperpoweredRecorderWrapped.h and SuperpoweredRecorder.h.
I create a SuperpoweredRecorder object as property named _wrapped and in my methods, I call the corresponding method of the _wrapped object.
With that, when I'll call start of a SuperpoweredRecorderWrapped in my Swift code, this one will call start of _wrapped, a SuperpoweredRecorder object. See the trick ?
And finally I include all the wrapped classes in my Bridging-Header, like that I can instantiate my wrapped objects from Swift.
NOTE: All the C++ code HAVE to be in .mm files, that's why I make my #include of .h that contains C++ code in my .mm file and not in my .h file.
I haven't programmed in Objective-C++, but I do have experience with C, C++, Objective-C, and Swift, so here are some observations and ideas based on looking at the Superpowered SDK and sample code.
A bridging header lets Swift interface directly with Objective-C, and since Objective-C is a strict superset of C, this implies interfacing with C as well. However, you cannot interface directly with C++, and that's where Objective-C++ comes to the rescue. From what I'm seeing you can mix Objective-C and C++ code in Objective-C++, which allows Objective-C to use C++ classes.
Now on to some specifics.
The bridging header in the SuperpoweredFrequencies example that you looked at introduces a new Objective-C class, Superpowered, which is not part of the library, but of the example, and is implemented in Superpowered.mm. It is an Objective-C++ file, because Superpowered calls some C++ code.
Looking at Superpowered.mm, you will see that it imports Objective-C headers:
#import "SuperpoweredFrequencies-Bridging-Header.h"
#import "SuperpoweredIOSAudioIO.h"
as well as C and C++ headers:
#include "SuperpoweredBandpassFilterbank.h"
#include "SuperpoweredSimple.h"
We could have used import instead of include for C++ code, too, but they are probably using include just to emphasize that it is C++ code. Looking at SuperpoweredBandpassFilterbank.h, we see that SuperpoweredBandpassFilterbank is a C++ class. It is used in Superpowered.mm by the Superpowered Objective-C++ class, see the filters member, which is a pointer to a SuperpoweredBandpassFilterbank object.
In the project you attempted to build, I see where the Superpowered interface is declared in the bridging header, but I don't see an implementation. The failure to #import SuperpoweredRecorder.h is due to SuperpoweredRecorder.h being a C++ header. The #include should be in your Objective-C++ (.mm) file, it's useless in the bridging header, since Swift can't make sense of C++ anyhow.
Hopefully this is helpful. Welcome to the world of C++.
I'm a bit surprised that you would have to provide prototypes of method.
I used Objective C libraries in my Swift project before and I only had to add the header files in my bridging header.
See example from my project. The bridging header contains just that:
// Use this file to import your target's public headers that you would like to expose to Swift.
//
#import "QTouchposeApplication.h"
#import <FBSDKCoreKit/FBSDKCoreKit.h>
#import <FBSDKLoginKit/FBSDKLoginKit.h>
#import <VungleSDK/VungleSDK.h>

programmatically calling functions from type library

I need to import a type library (it's actually an .exe that gives access to a COM interface implementation).
The thing is that i want to do that but with the MinGW compiler and not VSC++.
There are many topics and threads on SO that explain the difference between the two #import directives, but the main idea is that we can't import type libraries with the MinGW import.
So why not try to load the type library programmatically at runtime using the
LoadTypeLibrary function and the ITypeLib interface.
Except that ITypeLib is rather used to describe the objects stored in the type library.
Now i have run on my .exe code similar to the one in this link here
to retrieve information about my .exe's methods and it shows what i expected (the same information i found in the generated .tlh with vc++)
Is there a way to call directly the library's functions ?? If yes :
Should I use the IDispatch::Invoke method ?
Is there a necessity for binding functions in the type library or mapping the class members (using ITypeComp::Bind) ?
Is there any way to convert the generated .tlh and .tli with vc++ into a normal .h & .cpp file and be able to use it with mingw compiler?
Thank you for your precisions !

Get functions/objects of imported .tlb

I've got a program which shipped with a .tlb file to access some functions/objects (read variables etc.) with my own C++ program. I did a search and imported the .tlb file with:
#import "MyLib.tlb" named_guids no_namespace
I can also import it by using the libid from oleview.exe (ProgId does not work).
Even if I get some warnings (as follows), my program still runs:
C4278 ['TextOut', 'CreateEvent', 'DeleteFile'] is already a macro; use the 'rename' qualifier
But.. how can I gain access of the functions/objects now?
Sorry I'm a beginner so please be patient.
Does it work somehow with IDispatch? Do I need to import some more dll's or do I need more #include directives?
I'm using Visual C++ 2008 Express.
--
Edit: Ok sorry, I already have access to the header of the objects (I see "Application" in auto completion) but I have no idea how to get the objects.
Object Overview
And I think I found the related wikipedia article.
Importing type library gives you description of all the interfaces and identifiers of that library. Normally you should not include additionally any header files. You should just normally create these interfaces using COM smart pointer and call their methods:
CComPtr pInterface;
pInterface.CoCreateInstance(__uuidof("ClassNameFromTLB"));
pInterface->CallMethod();

How do I create interface methods using .tlb types in VS C++?

Background:
The .TLB file contains interfaces written in language 'X'. I don't have .h, .idl, .tlh, or any other header files - just the .TLB file. Language 'X' does not export compatible .h, .idl, etc.
I use the VS wizard to add an ATL simple object to my ATL project.
I want to add a method to the interface of my simple ATL object that uses one of the .TLB defined types for a parameter.
// Something like the following in the .idl file:
interface ISomeInterface : IUnknown {
HRESULT SomeMethod([in] ITypeFromTLB* aVal); // ITypeFromTLB declared in .TLB file.
};
How can I do this? I'm hoping for a wizard, or a line in the .idl interface declaration that would bring in the .tlb information. midl's include (no .tlb), import (no tlb), and importlib (library only) don't seem to provide a solution (I need proxy/stub to be working, so I cannot put this inside the library declaration with the importlib command).
Use #import in cpp/h to bring TLB interfaces to your namespace.
On Visual Studio command line do oleview. Then File -> View Type Lib, give it full path to your foo.tlb. Now in ITypeLib Viewer do File -> Save As .. and you can export all 3 (.h, .idl, .c) from there.

#import'ing msado15.dll, is there another way?

In all ADO C++ code I can find, there is a line
#import "C:\Program Files\Common Files\System\ADO\msado15.dll" no_namespace rename("EOF", "EndOfFile")
I understand that this line "incorporate information from a type library", and that "The content of the type library is converted into C++ classes". What?
I'm also looking for the header file for ADO C++, but I can't seem to find it.
It's been a while since I played with that stuff, so what follows is a bit vague and may even be slightly inaccurate, but I hope it still helps:
The DLL implements COM interfaces, and contains a type library describing those interfaces. Among other things, a type library contains the IDL of those interfaces, which should be compiled to generate C++ header files that your program can use.
The #import directive automates the process of extracting the TLB from the DLL and compiling the interfaces it describes to generate the corresponding C++ headers, and #include-ing the generated headers.
#import will generate the header file for you. In this case have a look for msado15.tlh in the intermediate directory (ie, projectname/debug).