Can I use LoadLibrary inside my Win32 DLL? - c++

Question

I have a device DLL Library "Device.DLL", I want to do a mask library of it "Mask.DLL". I only have the device DLL, not .lib.
My code:
// Load library
hLibHandle = LoadLibrary(L"Device.dll");
// GetProcAddress for my function
myDeviceFunc = (lpmyDeviceFunc)GetProcAddress(hLibHandle, "myDeviceFuncName");
// Calling function
myDeviceFunc();
This works very well in a Console Application, but no inside my Win32 DLL. When I run my MyDeviceFuncMask() from my Mask.DLL I get "Application has stopped working".
MyDeviceFuncMask() just do this:
EXPORT_DEFINE int MyDeviceFuncMask() {
// Load library
hLibHandle = LoadLibrary(L"Device.dll");
// GetProcAddress for my function
myDeviceFunc = (lpmyDeviceFunc)GetProcAddress(hLibHandle, "myDeviceFuncName");
// Calling function
int result = myDeviceFunc();
return result;
}
I've exported anothers functions and the DLL works well, for example:
EXPORT_DEFINE int TestFunc() {
return CONST_SUCCESS;
}

Answer 1

It's highly likely that your LoadLibrary call is failing, but there's not enough information here to diagnose it. So here's a list of reasons why LoadLibrary can fail:
It can't find the library. Read the documentation about naming, search order, etc.
The library is for the wrong architecture. For example, a 32-bit process cannot load a 64-bit DLL.
You're trying to load the library from DllMain, which will fail because the loader is holding the loader lock during DllMain to prevent the possibility that DLLs get loaded before the DLLs they depend on.
The DLL's DllMain returns FALSE from the DLL_PROCESS_ATTACH callback.
The DLL tries to do something in its DllMain that it shouldn't be doing (like calling LoadLibrary).
A transitive dependency of the DLL you're trying to load failed to load (for any of the previous reasons). For example, if you try to load foo.dll, and foo.dll is linked against bar.dll, then the loader will first try to load bar.dll, and perhaps that's what's failing.
In addition to outright failure, it's also possible to load the wrong DLL accidentally if the name conflicts with another DLL that's already loaded into the process. If you try to load foo.dll, but another foo.dll is already loaded into the process, you'll just get a fresh handle to the already loaded one. I believe you can load two DLLs with the same name only if you load it with an absolute file path.
If you do end up with a handle to the wrong DLL, that will likely result in the failure of a subsequent GetProcAddress. You can diagnose this quickly in the debugger by putting a breakpoint on your LoadLibrary call and then searching the OutputWindow to see whether another DLL of the same name has already been loaded. (But, really, you should be checking the return values of LoadLibrary and GetProcAddress anyway.)
I've made this a community wiki so others can add reasons why LoadLibrary can fail, and we can direct people here when they post questions about LoadLibrary failures.