I am new to c++ and this code always returns NULL even though i know the file exists:
HMODULE hModule = GetModuleHandle(TEXT("C:\\Users\\Steve\\Desktop\\stub.exe"));
Interestingly, if i copy stub.exe to C:\Windows\system32, it finds the module with this code:
HMODULE hModule = GetModuleHandle(TEXT("stub.exe"));
Am i missing something incredibly basic?
You can only call GetModuleHandle(L"C:\\Users\\Steve\\Desktop\\stub.exe"); when you're running C:\Users\Steve\Desktop\stub.exe.
But in general, you don't call GetModuleHandle for your EXE name. Since there's only one EXE per process, you just call GetModuleHandle(0).
Firstly, GetModuleHandle requires that you load the dll into the process before hand.
Windows has specific paths that it uses to search for modules, as well as some switches to force 'safe' dll loading, you may want to look into SetDllDirectory and AddDllDirectory if you wish to expand the locations searched. See this for an explanation of how Windows search for binaries.
Here is a quote from MSDN:
GetModuleHandle Function
Retrieves a module handle for the specified module. The module must have been loaded by the calling process.
This means that you have to load the module with LoadLibrary first. System32 might get special treatment, but you really should not be copying anything there. The folder is strictly for the operating system's usage.
Related
i think is very stupid, but I can't understand,
for example, I want use Windows API like GetWindowsDirectory, GetSystemInfo and etc... I can use Api directly or calling through GetProcAddress :
Method 1
here I can calling APIs with LoadLibrary and GetProcAddress :
#include <windows.h>
typedef UINT (WINAPI *GET_WIN_DIR)(LPWSTR lpBuffer, UINT size);
TCHAR infoBuffer[MAX_PATH + 1];
HINSTANSE dllLoad = LoadLibrary("Kernel32.dll");
GET_WIN_DIR function = (GET_WIN_DIR )GetProcAddress(dllLoad, "GetWindowsDirectoryW");
int result = function2(infoBuffer, MAX_PATH + 1);
Method 2
here I can calling directly APIs like GetWindowsDirectory :
#include <windows.h>
TCHAR infoBuffer[MAX_PATH + 1];
GetWindowsDirectory(infoBuffer, MAX_PATH);
I have 2 question :
What is the difference between the two methods above?
is it load Library impact on executable file?(.exe)(I did test, but it'snot changed)
Microsoft calls
Method 1 ... Explicit linking
Method 2 ... Implicit linking
From MSDN Linking an Executable to a DLL:
Implicit linking is sometimes referred to as static load or load-time dynamic linking. Explicit linking is sometimes referred to as dynamic load or run-time dynamic linking.
With implicit linking, the executable using the DLL links to an import library (.lib file) provided by the maker of the DLL. The operating system loads the DLL when the executable using it is loaded. The client executable calls the DLL's exported functions just as if the functions were contained within the executable.
With explicit linking, the executable using the DLL must make function calls to explicitly load and unload the DLL and to access the DLL's exported functions. The client executable must call the exported functions through a function pointer.
An executable can use the same DLL with either linking method. Furthermore, these mechanisms are not mutually exclusive, as one executable can implicitly link to a DLL and another can attach to it explicitly.
In our projects we use implicit linking in any common case.
We use the explicit linking exceptionally in two situations:
for plug-in DLLs which are loaded explicitly at run-time
in special cases where the implicit linked function is not the right one.
The 2nd case may happen if we use DLLs which themselves link to distinct versions of other DLLs (e.g. from Microsoft). This is, of course, a bit critical. Actually, we try to prevent the 2nd case.
No, I don't think it's stupid at all. If you don't understand, ask. That's what this site is for. Maybe you'll get downvoted, who knows, but not by me. Goes with the territory. No pain, no gain, ask me how I know.
Anyway, the main purpose of what #Scheff calls 'explicit linking' is twofold:
If you're not sure whether the the DLL you want to use to is going to be present on the machine at runtime (although you can also use /DELAYLOAD for this which is a lot more convenient).
If you're not sure if the function you want to call is present in (for example) all versions of Windows on which you want your application to run.
Regard point 1, an example of this might be reading or writing WMA files. Some older versions of Windows did not include WMA support by default (we're going back quite a long way here) and if you implicitly link to WMA.DLL then your application won't start up if it's not present. Using explicit linking (or /DELAYLOAD) lets you check for this at runtime and put up a polite message if it's missing while still allowing the rest of your app to function as normal.
As for point 2, you might, for example, want to make use of the LoadIconWithScaleDown() function because it generally produces a nicer scaled icon than LoadIcon(). However, if you just blindly call it then, again, your app wont run on XP because XP doesn't support it, so you would instead call it conditionally, via GetProcAddress(), if it's available and fall back to LoadIcon() if not.
Okay, so to round off, what's the deal with /DELAYLOAD? Well, this is a linker switch that lets you tell the linker which DLL's are optional for your app. Once you've done that, then you can do something like this:
if (LoadIconWithScaleDown)
LoadIconWithScaleDown (...);
else
LoadIcon (...);
And that is pretty neat.
So I hope you can now see that this question is really about the utility of explicit linking versus the inconvenience involved (all of which goes way anyway with /DELAYLOAD). What goes on under the covers is, for me, less interesting.
And yes, the end result, in terms of the way the program behaves, is the same. Explicit linking or delay loading might involve a small (read: tiny) performance overhead but I really wouldn't worry about that, and delay loading involves a few potential 'gotchas' (which won't affect most normal mortals) as detailed here.
I am porting a DLL from Windows to Linux (OS X actually).
I used this StackOverflow article to do that change.
i.e. I've ported the Windows "bool DllMain()" to the Linux way:
__attribute__((constructor)) void dllLoad();
__attribute__((destructor)) void dllUnload();
... but both are void return types. I need to be able to do the same as Windows and return FALSE if a condition isn't met in the constructor so that the dlopen() fails and the .so doesn't load.
How do I get the calling dlopen() to fail?
The answer is that it isn't possible.
As stated above you can't error out in the constructor - be it an exception or exit()
You need to approach this differently.
If you are dynamically loading a library, than you must also be using GetProcAddress() and dlsym() to actually do anything with it. dlsym() is your path forward here.
You clearly control the plugin's code, since otherwise you couldn't even add these APIs to it. So, all your 'dllmain' on either platform needs to do is set some global 'is valid' state information. You then simply call a known API like "ModuleIsValid()" whose entire job is to simply read that state info & return true/false. If it returns false, you close the library and report failure.
I have a DLL given named Lib.ddl. In the dll i have a function named add that takes an integer as a parameter.
Using the windows API and by using the following class.
class WindoswAPI
{
public:
WindowsAPI();//constructor
//helper functions
~WindowsAPI();
private:
}
How do I load this library in the constructor of the class. Extract the function via helper functions, and unload the function in the destructor?
I have looked on the internet for solutions and help but i cant find any.
You should first look at LoadLibraryEx() in order to load the dll in your process, then you can use GetProcAddress() to obtain a pointer to a function by name. Note the HMODULE parameter requested from the second function is returned by the first. You have to carefully know the function signature to invoke it without causing GPFs, so don't be surprised if you have to do some debug before having it working.
First easy thing to check anyway are the return values of both functions: the first one should return something different from zero ( it actually returns the virtual address where the dll is loaded ), if it returns NULL, use GetLastError to have some hints.
The same for GetProcAddress, if it return zero something didn't work, and usually is the incorrect spelling of the function name. As I said before having back an address from GetProcAddress does not guarantee you have finished: you must know perfectly how to call the function. If you need help in discovering which name are exposed from the dll, you will find useful DUMPBIN.EXE, you should have it already available from the Visual Studio Tools command prompt.
When your code finish with the dll, you can try to unload it by using FreeLibrary().
Look at POCO C++ Libraries, it contains very nice crossplatfrom DLL-Loader to avoid hand-written workarounds and boilerplate.
I'm programing on C++, I'm using Visual Studio 2008, Windows XP, and I have the following problem:
My application, that is a DLL that can be used from Python, loads an external dll, uses the required methods, and then unloads this external Dll.
It's working properly, but after more than 1000 cycles the method "LoadLibraryA" returns a NULL reference.
The main steps are:
HINSTANCE h = NULL;
h = LoadLibraryA(dllfile.c_str());
DWORD dw = GetLastError();
The error got is:
ERROR_DLL_INIT_FAILED
1114 (0x45A) A dynamic link library (DLL) initialization routine failed.
The Dll is unloaded by using the following:
FreeLibrary(mDLL);
mDLL = NULL;
Where mDLL is defined like this:
HINSTANCE mDLL;
First alternative tried:
Just load the Dll only once, and unloaded it when the application ends. This fix the problem but introduces a new one.
When the application ends, instead of first executing the DllMain method of my applicaion, wich unloads the external DLL, is executing first the DllMain method of the other Dll. This cause the following error because my application is trying to unload a Dll that was unload by itself previously.
"Unhandled exception at 0x04a00d07 (DllName.DLL) in Python.exe: 0xC0000005: Access violation reading location 0x0000006b".
Any suggestion will be welcomed.
Thanks in advance.
Regards.
Make sure that initialization code of the loaded/unloaded library doesn't leak memory. Many libraries expect to be loaded only once and not always clean up their resources properly.
E.g. in C++ file at the top level one can declare and initialize a variable like this:
AClass *a = new AClass(1,2,3);
The code would be executed when library is loaded automatically. Yet, now, it is impossible to free the hanging instance as library doesn't know precisely when/how it is going to be unloaded. In the case one can either replace "AClass *a" with "AClass a" or write your own DllMain for the library and free resources on DLL_PROCESS_DETACH.
If you have no control over the library's code, then it might make sense to create a cache of loaded libraries and simply never unload them. It is very hard to imagine that there would be unlimited number of libraries to overload such cache.
I have a native DLL that is a plug-in to a different application (one that I have essentially zero control of). Everything works just great until I link with an additional .lib file (links my DLL to another DLL named ABQSMABasCoreUtils.dll). This file contains some additional API from the parent application that I would like to utilize. I haven't even written any code to use any of the functions exported but just linking in this new DLL is causing problems. Specifically, I get the following error when I attempt to run the program:
The application failed to initialize properly (0xc0000025). Click on OK to terminate the application.
I believe I have read somewhere that this is typically due to a DllMain function returning FALSE. Also, the following message is written to the standard output:
ERROR: Memory allocation attempted before component initialization
I am almost 100% sure this error message is coming from the application and is not some type of Windows error.
Looking into this a little more (aka flailing around and flipping every switch I know of) I linked with /MAP turned on and found this in the resulting .map file:
0001:000af220 ??3#YAXPEAX#Z 00000001800b0220 f ABQSMABasCoreUtils_import:ABQSMABasCoreUtils.dll
0001:000af226 ??2#YAPEAX_K#Z 00000001800b0226 f ABQSMABasCoreUtils_import:ABQSMABasCoreUtils.dll
0001:000af22c ??_U#YAPEAX_K#Z 00000001800b022c f ABQSMABasCoreUtils_import:ABQSMABasCoreUtils.dll
0001:000af232 ??_V#YAXPEAX#Z 00000001800b0232 f ABQSMABasCoreUtils_import:ABQSMABasCoreUtils.dll
If I undecorate those names using "undname" they give the following (same order):
void __cdecl operator delete(void * __ptr64)
void * __ptr64 __cdecl operator new(unsigned __int64)
void * __ptr64 __cdecl operator new[](unsigned __int64)
void __cdecl operator delete[](void * __ptr64)
I am not sure I understand how anything from ABQSMABasCoreUtils.dll can exist within this .map file or why my DLL is even attempting to load ABQSMABasCoreUtils.dll if I don't have any code that references this DLL. Can anyone help me put this information together and find out why this isn't working? For what it's worth I have confirmed via "dumpbin" that the parent application imports ABQSMABasCoreUtils.dll, so it is being loaded no matter what. I have also tried delay loading this DLL in my DLL but that did not change the results.
EDIT
I have double checked and all files involved are 64 bit.
I just had exactly the same problem. This is an issue with the Abaqus API rather than with the loading of DLLS.
I think it is because the Abaqus API overrides the new and delete functions (as you seem to have noticed). If you call new or delete in your program before initializing the Abaqus API, such as by calling odb_initializeAPI(); then you get the
ERROR: Memory allocation attempted before component initialization
error message and the program crashes.
In my program, calling odb_initializeAPI(); before the first new resolved the problem.
Well, sure you'll reference the imports of that library. Hard to write a C++ program without using the new or delete operator. Dealing with 3rd party software that thinks it needs to override the CRT version of those operators is hard enough, impossible when it won't allow you to call them until it thinks the time is right. Abandon all hope or seek help from the vendor.
One of the possible reason of an error during loading of ABQSMABasCoreUtils.dll is that some dependency module (inclusive delayed load DLLs) could not be found. Use Dependency Walker (see http://www.dependencywalker.com/) to examine all dependencies of ABQSMABasCoreUtils.dll.
I have two suggestions:
Verify that you can load ABQSMABasCoreUtils.dll with respect of LoadLibrary. You don't need call any function from ABQSMABasCoreUtils.dll. Usage of LoadLibrary I don't see as the end solution. It' s only a diagnostic test. With the test you can verify either you have some general problem of loading ABQSMABasCoreUtils.dll in your program or you have some kind of process initialization problem.
If loading of ABQSMABasCoreUtils.dll with respect of LoadLibrary will failed, then use profiling feature of Dependency Walker to protocol of all calls done during loading of ABQSMABasCoreUtils.dll. One other way would be usage of Process Monitor (see http://technet.microsoft.com/en-us/sysinternals/bb896645.aspx) to trace what file and registry operations will be done during loading of ABQSMABasCoreUtils.dll.
If LoadLibrary is not failed, then you have really an initialization problem of DLLs. Typically the problem exist if a DLL inside of DllMain try use a function from another DLL which is not yet initialized (not yet returns from DllMain). Before one start diagnostic of this problem, we should try to exclude a more simple problems with LoadLibrary.
The ABQSMABasCoreUtils.dll looks like it's importing 64-bit functions. Is your dll also 64-bit? If not, then that's the problem - you cannot mix DLLs compiled for different architectures in the same process.