CODEWITHSUNDEEP
delphiexceptiondlldelphi-2009
Wodzu
Wodzu

Reputation: 6979

External exception is thrown in function when using DLL's from not application folder

I have a problem which I do not understand. I am using a DLL in my application. This DLL requires other DLL's and I have all of them. If I put the libraries in my appliction folder everything works fine.

However, having a bunch of DLLs in application folder looks quite ugly so I wanted to move them to application\lib subfolder.

After this change now I am getting External Exception when I try to use some of its functions.

I've only changed one line of code:

The original code

DLLHandle := LoadLibrary(Pchar(ExtractFilePath(ParamStr(0)) + 'External.dll'))

The code after change

DLLHandle := LoadLibrary(Pchar(ExtractFilePath(ParamStr(0)) + 'lib\External.dll'))

In both cases DLLHandle have a handle after loading the library. I am also not getting any error after calling GetProcAddress( DLLHandle, '_SomeFunction@8')

No exceptions, and return value of GetLastError is always 0.

Do you have any idea what could be wrong?

Thanks.

Upvotes: 2

Views: 1869

Answers (2)

David Heffernan
David Heffernan

Reputation: 612954

Life is far easier if you keep the DLLs in the same folder as the executable. That's the first folder searched when libraries are loaded. To move all the DLLs into a sub folder of the executable directory requires cooperation from all DLLs.

Most likely you have secondary DLL dependencies that are not cooperating. So exe loads A fine, but then A fails to load B. You can debug this further with Dependency Walker running in profile mode. It's quite possible that a secondary DLL is being loaded with implicit linking and that this throws and exception. Whatever the cause, Depenency Walker will lead you to the problem.

Whilst you can modify the PATH variable this is generally not advisable. If you do choose to go down this route then don't modify system wide, just modify the executable process environment at runtime before the first LoadLibrary. This is tenable so long as all your DLL linking is explicit using GetProcAddress.

All accepted wisdom recommends that you put your DLLs in the same folder as your executable. I would echo this recommendation. If you did this then you would be able to use implicit linking which would greatly simplify your code.

Yet another option may be to abandon DLLs and link everything straight into your executable. Unless you have a plugin type architecture, a single big exe is by far the simplest approach.

Upvotes: 3

Steve
Steve

Reputation: 1865

The other DLL's that need to be loaded must be on the system path for Windows to find them. Your application can find the External.dll as you explicitly define the path. Try adding the lib folder to your system path.

Upvotes: 1

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