CODEWITHSUNDEEP
c++conventions
Scott Smith
Scott Smith

Reputation: 3986

Best practice when producing a C++ static or dynamic library for others?

I'm providing a Microsoft C++ library (static and dynamic) for other clients in my company. My library has a few classes that depend upon functions located in common Windows DLLs whose import libraries aren't included in the project link settings by default.

Rather than add a new import library name to the linker section of every build configuration of my library each time a new dependency like this came up, I thought it would be better in terms of encapsulation of dependencies (and a bit more self-documenting) if I used #pragma comment(lib, ...) in the .cpp file of the class that depended upon a function from such a DLL, e.g.:

Foo.cpp:

#include <SomeWinLib.h>

#pragma comment(lib, "somewinlib.lib")

... implementation of Foo class ...

...but I found that this was causing link warnings/errors for clients of my library if they were also using SomeWinLib. After doing some reading on the subject, it seems that the recommended/best practice is to let the client who is linking in my library also link in the libraries it depends upon.

I still wanted this to be as automatic/painless as possible for the clients, so rather than just put a list of required import libraries in a readme.txt file (and then sit back and wait for the inevitable phone calls from frustrated developers), I'd just place the #pragma comment in the Foo.h header file. That way, clients would automatically link in the required library if they included the header file of a class that required it.

Foo.h:

#pragma comment(lib, "somewinlib.lib")

public class Foo
{

However, when I build my library, Foo.cpp includes Foo.h obviously, so it would seem that I need some kind of preprocessor "guard" around the #pragma comment line in the header file so that it's only seen by the preprocessor when clients include my header file.

Foo.h:

#if !defined(building_my_library)
  #pragma comment(lib, "somewinlib.lib")
#endif

public class Foo
{

All of this seems like something that pretty much EVERY library must be doing, yet I don't see examples of this when I Google other open source Windows libraries. That makes me suspect I've missed something somewhere.

Does anyone know if I'm understanding the issues correctly, and if so, whether I'm over-complicating the solution?

Thanks!

Upvotes: 0

Views: 1109

Answers (2)

Miles Budnek
Miles Budnek

Reputation: 30494

Your last option is more or less what the boost headers do, except they also provide a preprocessor directive to explicitly turn off the auto-linking in case you want to control things yourself:

#if !defined(building_my_library) && !defined(no_auto_link_stuff)
    #pragma comment(lib, "somelib.lib")
#endif

Upvotes: 1

paddy
paddy

Reputation: 63451

A solution that you might not have considered is to use runtime linkage to the DLL via LoadLibrary and GetProcAddress, removing the dependence on somewinlib.lib.

Upvotes: 1

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