CODEWITHSUNDEEP
c++visual-studioqtwinapimingw
earth
earth

Reputation: 955

Why does MSVC need an import library (.lib) for a .dll when MinGW doesn't?

I'm a little confused as to why a 3rd party .dll I'm using comes with a .lib file labeled as an "import library." When I run the program, I just place the .dll in the same directory as the executable and it works. I'm using MinGW.

Could someone explain why the .dll comes with a .lib import library if I don't even need it? How would I even use it and where should I put it if I did use it with MinGW?

I read up on it and it looks like the .lib file is not needed by MinGW (what I'm using) and is needed by MSVC. Why is this?

P.S. If I wanted to put a .dll in a directory other than the directory containing the executable, could I put a line in the .pro file to point to it?

Upvotes: 1

Views: 652

Answers (1)

ivan_pozdeev
ivan_pozdeev

Reputation: 36036

According to http://www.mingw.org/wiki/sampleDLL, MinGW can guess the information that's contained in a .lib (DLL name, exported entries' names and ABI) from the corresponding .h file and the DLL itself.

According to http://www.mingw.org/wiki/CreateImportLibraries, this works "for all DLLs created with MinGW and also a few others".

In cases when it can't guess correctly, you still need to provide a .lib file. The latter link has instructions on how to generate one by hand if you haven't got a pristine one.

The former link refers to ld docs for a more in-depth description. Specifically, it's at the ld and WIN32 (cygwin/mingw) node, "direct linking to a dll" section. Among other things, it outlines cases when a .lib is necessary:

  • until recently, direct linking didn't work for exported data entries
  • if a .lib contains pure static objects (e.g. cygwinX.dll)
  • if exported entries do not conform to mangling rules (e.g. Win32 libraries)

Upvotes: 3

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