How to get an error message box when LoadLibrary fails? - c++

Question

I want the proc to show detailed information such as which dependency is missing, whether the dll is invalid...
int main(int argc, char *argv[]) {
// Record original error mode
UINT prevErrorMode = GetErrorMode();
::SetErrorMode(0);
std::wstring wstr;
// Get library absolute path and store into wstr.
// ...
typedef int (*EntryFun)(int, char *[]);
HINSTANCE hDLL = ::LoadLibraryW(wstr.data());
int res = -1;
if (hDLL != NULL) {
EntryFun fun = (EntryFun)::GetProcAddress(hDLL, "main_entry");
if (fun != NULL) {
// Restore error mode
SetErrorMode(prevErrorMode);
res = fun(argc, argv);
} else {
res = ::GetLastError();
::MessageBoxW(nullptr, TO_UNICODE("Failed to find entry!"), TO_UNICODE("Error"),
MB_OK | MB_ICONERROR);
}
::FreeLibrary(hDLL);
} else {
res = ::GetLastError();
::MessageBoxW(nullptr, TO_UNICODE("Failed to load main module!"), TO_UNICODE("Error"),
MB_OK | MB_ICONERROR);
}
return res;
}
I use SetErrorMode but it doesn't seem to work, there's no message box after LoadLibrary returns NULL.
Also, FormatMessage doesn't help because it cannot provide information about which dependency is missing.

Answer 1

LoadLibrary reports error through GetLastError. The advantage of Run-Time Dynamic Linking is Run-time dynamic linking enables the process to continue running even if a DLL is not available. You may write your own loader to walk through the dependencies yourself until you find what is missing as #RemyLebeau said. There is a MemoryModule repository which loads a DLL completely from memory and you can refer to.
But for Load-Time Dynamic Linking, the system simply terminates the process if it cannot find the DLL.