In my source I have:
#pragma comment(lib, "ldv32.lib")
Originally this was:
#pragma comment(lib, "ldv32")
When I build and then try to register the DLL it fails:
I used "Dependency Walker" to look at the DLL and I could see that it was trying to open LDV32.DLL, so I then edited the project and modified the pragma. Cleaned and Rebuilt project, however it still fails and "Dependency Walker" still reports that the DLL is looking for LDV32.DLL
How do I fix this, I've checked the path and project build, the location of the LIB is specified but why is it looking for a DLL and not the LIB?
The library ldv32.lib is an import library. It resolves the externals that are used in your DLL module. But it implements only small stubs. When the module is loaded with LoadLibrary, some code in the the ldv32.lib tries to load the DLL ldv32.dll that implements the actual functionality.
You should lookup the Echolon OpenLDV DLL "ldv32.dll" and copy it in the folder where the process is loaded from. If you share your program or DLL make sure to include that DLL.
You can also check if a static LIB exists. In that case you can link with that.
Related
I have some DLLs that I want to use in a FORTRAN Project in VISUAL STUDIO but I can't find how.
Here is a simple code I'm using to find out how.
Using visual studio I created a DLL from this
subroutine printing
!DEC$ ATTRIBUTES DLLEXPORT::printing
print*,"dll naimi created"
end subroutine printing
I added the link of the DLL to project>properties>Linker>General>Additional Library directories
Main program:
program Console11
implicit none
call printing
end program Console11
ERROR : Error 1 error LNK2019: unresolved external symbol _PRINTING referenced in function _MAIN__.
other solutions related to this suggest using the .lib created while generating the DLL, but in my real case I only have the DLLs without their .lib.
So how to use a DLL ... ?
You appear to be trying to use a DLL as an input file to the linker.
(You also appear to be trying to specify a file for a linker option that takes a directory. To specify an additional input file for the linker, either add the file to the project just like you would attach a source file, or use the "Linker > Input > Additional dependencies" project property. The property you mention in your post then tells the linker where (which directories) to search for those additional dependencies.)
Unlike the unix convention, you do not link against DLLs when building executables and other DLLs on Windows. The DLL typically does not contain the necessary information for the linker - instead that information is contained in an import library (which is just a variation of a typical .lib static library) or equivalent.
If you were able to successfully build a DLL, then you will probably find the import library for that DLL in the same directory as the DLL. Supply that import library as an additional dependency for projects that require the DLL.
When you link an EXE or other DLL using an import library on Windows, the target DLL is automatically loaded by the operating system when your executable code is loaded. This is called load time dynamic linking.
If you do not have the import library for a DLL, then your choices are:
Ask the person who built the DLL for the import library.
Reference the DLL using run time dynamic linking, rather than load time. This means that you use the Windows API functions LoadLibrary, GetProcAddress and friends in your program to explicitly tell the operating system to load a particular DLL and to obtain the address of a function pointer. If you are using Intel Fortran, then complete examples of this are installed with the compiler - see in the file "C:\Program Files (x86)\IntelSWTools\samples_2016\en\compiler_f\psxe\DLL.zip" or similar.
Generate an import library from the minimum information in the DLL, plus other information about the DLL that you may have. One approach to this is to write a module definition file (.def) for the DLL, and then use the LIB utility to turn that def file into an import library. See How to make a .lib file when have a .dll file and a header file for an example.
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 have two existing executables A and T, in the same solution that both ran just fine before I touched them. In executable A is a header defining a class P, and a prototype for a static instance MyP. The definitions are compiled in project A. In executable T, I wanted to call member functions of MyP in project A, so I added dllimport/export macros to the declarations of the class and MyP in the headers (not at the definitions), and included the headers in project T. The dllimport/export macros are standard, and A_EXPORTS is defined in project A, but not in T.
#ifdef A_EXPORTS
#define A_API __declspec(dllexport)
#else
#define A_API __declspec(dllimport)
#endif
//various definitions and includes, defining ENUM_RECORDING_TYPE and ERROR
A_API HFILE viosopen(const _TCHAR *path, ENUM_RECORDING_TYPE rt, int flags);
A_API struct P {
ERROR B(SHORT phraseNum);
};
A_API extern P MyP;
I added project A as a dependency on project T in the solution. A still compiles fine, but T comes up with unresolved external symbol "__declspec(import) <snip> referenced in function <snip> for the function calls, and unresolved external symbol "__declspec(dllimport) class P MyP" <snip> for the static object. I also see in the output log, right after it starts linking: Creating library Debug/A.lib and object Debug/A.exp which seems ominous since it's supposed to be linking against the existing executable.
My question is: how can I tell MSVC 2010 where those are? I thought simply setting A as a dependency would have it figure that out automatically. I can link against the existing executable, right?
To statically link your program you don't need the __declspec() stuff and you don't need a separate project to create a LIB file. I think you can just link using the .obj file from your A project.
Your A project has a header file and presumably has a .cpp file that contains the implementation of the items described in that header. Let's say your header file is foo.h and the associated implementation is foo.cpp. When compiled, there should be a foo.obj intermediate file in the <solutiondir>\A\Debug or <solutiondir>\A\release intermediate folder. That file can be used by the linker.
In project T's properties, find Linker | Input and change the "Additional Dependencies" property to include the foo.obj file. One approach would be to use a relative file path to locate the file - for example ..\A\Debug\foo.obj in your debug configuration. Another approach is to use the simple file name in "Additional Dependencies" - foo.obj - and then use Linker | General | Additional Library Directories" to help the linker find the file - e.g., ..\A\$(IntDir). Using the $(IntDir) macro has the advantage that the same value works for Debug and Release settings.
Remember to set up a build dependency from your T project to your A project to be sure the A project is compiled first. Otherwise the foo.obj file might not exist when the T linker comes to look for it. In the Solution properties, select Project Dependencies and then set Project T depends on Project A.
To dynamically link you need to use the A.LIB file as #ajay said. The __declspec(DllImport) tells the compiler what functions and data you are importing but doesn't tell it where you are importing those things from.
Using the A.LIB file as input to the linker is much the same as using the foo.obj file in the statically linking case except that the lib file ends up in the solution output directory <solutiondir>\Debug instead of the project intermediate directory <solutiondir>\A\Debug.
This walkthrough on creating and using a DLL might be useful background.
I asssume project A is DLL not an EXE, which is successfully producing a LIB file.
You need to use the A.LIB as Linker Input in project B. Just producing LIB file wont make other projects automatically link to it.
I am banging my head against a wall here.
All i want is to link a static .lib file in a cpp windows forms application! So, i have an include folder in my project folder that holds header files for that .lib (lib is Yaml-cpp if someone wonders). And i have a lib folder that has the .lib files for that library.
I tested it on a blank project
1.I make a new windows forms project in VS2008, in C++.
2.I go to project properties - c/c++ general and additional include directories that have yaml-cpp header files
3.I go to linker and add path to my lib directory
4.I go to linker - input and add my .lib file
5.I check linker command line and it contains my .lib file so it must be all set.
6.Then i write the sample code in an onbutton function body (which appears in form1.h fie).
Sample code is from here http://code.google.com/p/yaml-cpp/wiki/HowToParseADocument and its just as simple as:
#include <fstream>
#include "yaml.h"
and then:
std::ifstream fin("test.yaml");
YAML::Parser parser(fin);
YAML::Node doc;
while(parser.GetNextDocument(doc)) {
//do nothing yet
}
7.And then i compile and have 10 "unresolved externals".
I have looked into another project that uses same library, and it has exactly same directory structure, same name of .lib added in linker - input - additional dependencies, same .lib and .h files. And it works for that project- but it doesnt work for me.
What in the world is wrong?
EDIT: I tried making new windows 32 console application and it worked correctly. I then tried to make another fresh windows forms application and it failed.
It is confirmed now. Same steps for linking a library work in console application and fail in windows forms application. WHY?
What you've done seems correct from your explanation, let's do some blind troubleshooting.
Try giving full path instead of relative path for library path and additional include directories. (but as u said that the file is getting read, that should be the problem.)
If you are using a copy of original libyaml-cppmdd.lib and its include file, check whether the header file that gets included is of the same version as the lib.
Check whether there are any functions in any part of the code that is having a declaration but no definition.
Check whether you're accessing any private functions from the library.
Please read this Microsoft article on Troubleshooting UnResolved External Symbol error.
Hope it helps!
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.