Dynamically linked DLL is loaded immediately after

问题:

I've dynamically linked libhunspell.dll (HunSpell) to my application. It works, but there is a dumb problem which I don't know why it happens.

Even before I use LoadLibrary("path\\to\\libhunspell.dll"); to load it and use it, on the start of the application it attempts to load the library by itself. If I place the libhunspell.dll into the path where my main executable resides, it can load it, otherwise it reports an error, immediately after starting the application - This application has failed to start because LIBHUNSPELL.DLL was not found. Re-installing the application may fix this problem. and the application doesn't start.

I would understand if the LoadLibrary would use invalid path but this happens as soon as the executable runs, even before the first statement in WINAPI _tWinMain(HINSTANCE, HINSTANCE, LPTSTR, int) executes (I've tried to place a breakpoint and it doesn't even reach it, so this happens before).

So, as a result, I must place libhunspell.dll in the same folder as my application executable, and not in the path I want.

This is probably easy to fix although I don't what to look for.

So the question is - how do I avoid it loading it immediately and have it wait until I use LoadLibrary call?

Here is how I linked if it can help:

1) compiled libhunspell.dll in Visual Studio 2015 (I used /MT option to link it statically so it doesn't have VC++ Redistributable as a dependency).

2) created import library (libhunspell.lib) using implib.exe -a -c -f libhunspell.lib libhunspell.dll

3) linked that to the source .cpp unit which is using it using #pragma comment(lib, "libhunspell.lib") (it is RAD Studio 2010 so the .lib is required unlike newer versions).

4) later in the same .cpp used LoadLibrary to load this library and used it.

回答1:

By linking in the import stubs (libhunspell.lib) the OS will load the DLL for you as it is now a static dependency.

One approach would be specify the library as a delayload dependency: /DELAYLOAD:libhunspell.lib via the linker options. You can then call LoadLibrary on the DLL.

The only other option is to stop including the .lib in the linker step, making it truly a dynamic dependency.

回答2:

I assume you did Add to project a *.lib file for your DLL. That is a kind of "static" linkage done in the App initialization (prior to your forms are created). So it has two disadvantages.

1. You DLL must be in the same path as the Apps EXE file
2. Sometimes DLL file name is locked (can not be changed)

The advantage is that you do not need to do any coding for the DLL loading as the VCL do it for you ... so your app should not contain the LoadLibrary,GetProcAddress calls you just include the *.h file with propper import declarations ...

For dynamic linkage you need to remove the *.lib from your project and use WinAPI LoadLibrary + GetProcAddress for loading your DLL as josh poley suggested. Here an example:

• Builder C++ calling VC++ class

Beware there was/(is?) a bug in the GetProcAddress preventing from loading all the functions from your DLL in some cases. Especially if the DLL has old legacy mangling of names the count of functions is high and the DLL was created on compiler incompatible with the mangling in question.