VC++ code:
namespace Test { class __declspec(dllexport) A { public: void foo(); }; }
Took from library compiled in MS VC++:
A#Test#
The same in BCB6 C++:
#Test#A
What is it connected with?
What compiler options to set to record the namespace in front of the class? Because of this, BCB6 cannot link the library.
Searched on Google but didn't find anything.
Different compilers decorate/mangle exported symbols differently. There is no option to make BCB's compiler decorate/mangle its symbols the same way that VC++ does, and vice versa.
In any case, you can't use a pre-compiled VC++ .lib file in BCB at all, as .lib files are compiler-specific.
If the VC++ .lib is a static library, you would have to recompile the library's source code using BCB's compiler.
If the VC++ .lib is an import library for a DLL, can create a new BCB-compatible import .lib file, by using either:
BCB's COFF2OMF tool to convert the VC++ .lib file itself into a new file in BCB's OMF format.
BCB's IMPLIB tool, which can create a new .lib file from the DLL itself.
Related
I am trying to use a C++Builder 11.1.5 created DLL in MSVC 2022 C++ project. Both are 32bit. I can't build the DLL in MSVC as it uses some VCL objects.
My C++ Builder defines the external function thus:
extern "C" __declspec(dllexport) void __stdcall SetEnabled(bool val) {
...
}
MSVC uses a header to reference the function:
extern "C" __declspec(dllimport) void __stdcall SetEnabled(bool val) ;
I have created a .DEF file with the same name as the DLL, containing this:
LIBRARY MYTESTDLL
EXPORTS
SetEnabled
And I have generated a .LIB file from this .DEF file using MS lib.exe:
lib.exe /DEF:MYTESTDLL.def /out:MYTESTDLL.lib /MACHINE:x86
Finally, I have added MYTESTDLL.lib to my MSVC project in the Linker->Additional Dependencies section.
But, when I build the program, I get this error:
Error LNK2019 unresolved external symbol __imp__SetEnabled#4 referenced in function _WinMain#16
I've tried adding the ordinal (#4) to my .DEF file and rebuilding the .LIB file, but I still get the same error.
In a hex editor, I can that __imp__SetEnabled is in the .LIB file, but clearly not in a way that MSVC likes.
Have I missed a step somewhere? Is there anything obviously wrong with what I've done?
Changing the MSVC header used to reference the function to:
extern "C" __declspec(dllimport) void SetEnabled(bool val) ;
and adjusting the C++Builder DLL to export the functions using __cdecl resolved the issue. I didn't realize that the __stdcall exported functions need decorating in .DEF file.
That said, I find that the DLL is fine unless I try to execute code in it that uses the VCL. Then things don't work properly. I wonder if it's not possible to write a DLL in C++Builder containing VCL code for use in MSVC?
I've got a copy of the axtls library that I've compiled into a static library. I'm linking it into a DLL that I'm building, and some of the axtls functions (_MD5_Final, _MD5_Init and _MD5_Update) seem to be getting exported from my DLL. I'm trying to figure out how to stop that from happening.
My DLL is built with a .def file that doesn't list any of these functions. However, they are all declared as __declspec(dllexport) in axtls itself so I suspect that is why they're being exported.
I was wondering if there was a way to block export of these functions, using a .def file or similar? My DLL is going to be used as part of a public SDK, so it's not particularly good to be exposing internal functions like this.
I suspect removing the __declspec(dllexport) from the definitions in axtls might solve my problem, but I'd rather not go modifying upstream code if I can avoid it.
Whenever you have a static LIB file and see all it's exported functions in a DLL that uses this LIB file to build, the solution is simple:
Recompile the static LIB project without __declspec(dllexport) and then recompile the DLL project.
With a DEF file you cannot do that.
I am porting a C++ project from an old Borland compiler to VisualStudio 2008. This project uses a third party DLL that I don't have the source code for, so I am unable to recompile or modify it. The header file for the DLL defines functions along the lines of:
extern "C" {
void __stdcall Init(int a, int b);
}
However when I try to link to this DLL, VisualStudio says that it cannot find the function _Init#8. When I look at the DLL I find that the function name is _Init, and not _Init#8 (it seems that the DLL to predates Microsoft adding #8 to stdcall name mangling).
My question is: How can I call funcions in this DLL? Does VisualStudio simply not support these old DLLs, or is there a flag/setting that I'm missing. (I am aware that I could use the LoadLibrary/GetProcAddress functions to dynamically call the functions at run-time, but would prefer to not to.)
I didn't notice anything that would tell me whether you are doing 32 or 64 bit coding. MSDN has some information on how to create an import library based on a dll that you have no source for. This article is for making a 32 bit import library. CHEERS!
I have a small issue when it comes to writing a DLL in MSVC (the 2010 version in particular).
My program consists of the main part and a DLL. The DLL contains a function that is
__declspec(dllexport) int test_function(void) {
return 42;
}
The file is compiled using a DLL project (not using pre-compiled headers, I have chosen a empty DLL project). Now, when I want to list the exported symbols using the dumpbin tool, the test_function is not listed under exports. Is there a specific setting that forces __declspec(dllexport) to actually export symbols?
Any help is welcome. Thank you!
That should do it. If this is the whole code, check the following:
1) You are actually checking the correct dll. Look at the timestamp. Double-check the location and the name.
2) You are compiling the specified cpp (I take it your definition is in the cpp file). Just because the file is in the directory doesn't mean it gets compiled, make sure it is added to the project.
3) Make sure your function is not excluded from the compilation unit by preprocessor directives.
Also look for other symbols and try to see what differences are there between the symbols that get exported and your function.
If this fails, you should move __declspec(dllexport) to your .h file and the definition (without __declspec(dllexport) ) to your .cpp. It might not be exported because the compiler might try to optimize it out by inlining it.
I'm new to vc++. I've just built a software and it generated a .dll and a .lib. I need to use functions from this in my code. Do I need to link to both .lib and .dll to build my code? What project properties do I have to alter to do this linking?
Actually, you need only the .dll file. It contains all the necessary code and data to run it's functions. It also contains a table that links the symbolic names of the functions (e.g. the function PrintMe), their ordinals (the number of that function in the DLL) and their addresses in the DLL.
If you want to use only the DLL, you have to "manually" get the symbols resolved:
Let's say you want to use the function PrintMe of the DLL. What you had to do is to resolve it's name (PrintMe) or it's ordinal (PrintMe is the 1st function of the DLL) to it's address. For this, you could use LoadLibrary, GetModuleHandle and GetProcAdress from the Win32 API (aka Windows SDK). Additionally, this method allows you to load the DLL at runtime (see below).
The easier way is to use the MSVC(++) features __declspec(dllexport) and __declspec(dllimport), e.g.
// your DLL
__declspec(dllexport) void PrintMe()
{
printf("Hello World!");
}
// you project to use the DLL
__declspec(dllimport) void PrintMe();
The first one (dllexport) tells the compiler to export the function. The second one (dllimport) is the interesting one: It creates all the necessary code to be able to use the function from the DLL.
For this, you need the .lib file in your project (which wants to use the DLL). The .lib file contains information for the linker to resolve the symbol name (PrintMe) to its address in the DLL. Since the .lib is statically bound, the linker can make use of it - the DLL on the contrary is bound at runtime / loading time, so the linker cannot use it. (Yes, the information in the .lib file is redundant.). Note: You cannot change the whole DLL when using this method w/o rebuilding your project with the new .lib file. Some structure changes affect the addresses of the functions in the DLL, see this SO answer.
One last difference between using the Win32 API (LoadLibrary...) and the MSVC method via __declspec is the loading of the DLL. When you use LoadLibrary, the DLL is loaded at runtime, of course (so you can catch exceptions when it cannot be found and so on). The other method loads the DLL at loading time, so you program will terminate (will not run) when Windows cannot find the DLL.
When you create a project in VS, you can activate the "export symbols" checkbox at the end of a wizard (Win32 project). That gives you some examples of exported symbols. Additionally, it introduces a macro plus a preprocessor defition plus some directives that are very useful:
// DLL header
#ifdef _YOUR_DLL_EXPORTS
#define YOUR_DLL_API __declspec(dllexport)
#else
#define YOUR_DLL_API __declspec(dllimport)
#endif
YOUR_DLL_API PrintMe();
You now can use this header file to build you DLL as your DLL project has that _YOUR_DLL_EXPORTS definition (see project properties page, C++, preprocessor). The project that uses the DLL can use this header, too, but then must not have such a name defined. When you include the header file in the project in which you want to use the DLL, the macro is resolved to __declspec(dllimport). This instructs the linker to look for this function (which is found in the .lib file) and create all the necessary code to load the DLL at runtime and resolve the symbol name.