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The problem

Information on how linking works in detail are scarce. Also IDEs hide the details of compilation which is a real pain when you have some linking related problem with your project.

Usually C++ books tell me that

C++ code --> preprocessed c++ code --> object code

But they really do not go into too much detail on what an average developer should know about linking despite the fact, that linking errors are common. How should a fresh C++ programmer know how to tackle an error like the following?

XmlRpcSocket.o:XmlRpcSocket.cpp:(.text+0x48b): undefined reference to `WSAGetLastError@0'

But this question is not specifically about this problem (-lwsock32 solves it). The problem is the lack of general knowledge about linking. My university C++ lecturer talked about linking for the time of one slide with a few black-boxes on it.

Also, resources on how linking works are scarce and most of the people I know still considers linking as a black-box operation. What I have learned about linking is through experimentation, and kinda "picked it up along the way", but the problem with this approach is that it raises more questions than it answers.

For example: I know .LIB files are library files which are bundles of object files. Now, how should one build and use a .LIB file? When is it desirable to use .LIB file? When sould I build static .LIB files or ones that reference DLLs? When I link a .LIB file with my object files do everything gets copied in, or just the object files I use? When should I build DLLs/so files instead of linking statically? Do I have to learn about the inner structure of object files to solve common problems? What do I have to know about name-mangling? When is it relevant? Can I link several different standard libraries with my project if one of the dlls load the old msvcrt? etc.

The question

Obviously I don't expect an answer to all the above listed questions in one go. I just need to know where to start. Is there a resource like "What Every Programmer Should Know About Memory", which talks about linking? So, I need resources to learn from and your insight on which direction should I go to learn about the linking process.

What are the things every developer should know about linking?

stonemetal
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Klaufir
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  • The C++ language does not currently support modules and libraries, so such support is often done with implementation specific language extensions. Better ask same question for specific operating system and compiler. – Öö Tiib Aug 24 '12 at 22:59
  • The way its done is very similar in both posix and windows. You have .lib/.a files. You have .dll and .so files. You have _undefined reference_ errors on both systems. The object file format are different, but there is a lot of common ground. This question is not about the what official C++ docs say about linking, I know the standard says linking is _implementaion detail_. Its about the common practices of linking in the C++ world. – Klaufir Aug 24 '12 at 23:13
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    In windows you may have to write things like `__declspec(dllexport)` into C++ code, in unix it may be something like `__attribute__ ((__visibility__("default")))` for supporting correct linking. – Öö Tiib Aug 24 '12 at 23:21
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    Please, if you want answers to explain how linking works, just ask the question "how does linking work in C++". You really don't need to write an entire novel about all the things you personally already know and the problems you have faced which reminded you of your uncle from Kentucky who once ... and so on. It's all irrelevant and it only serves to dilute the question and make people want to close it. I won't edit it for you because it'd be a major change, but I really believe you'd get much better answer if you just stuck to your question, without the exposition – jalf Aug 24 '12 at 23:48
  • Alright. Followup to this question: http://stackoverflow.com/questions/12122446/how-does-c-linking-work-in-practice – Klaufir Aug 25 '12 at 13:36

4 Answers4

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There are TONS of resources.

I guess that might be overwhelming for a "beginner" ;)

As far as "Windows", you could do worse than to start here:

I'd also recommend this:

'Hope that helps :)

PS:

As clarification:

  • You want to know how the bits you've "compiled" (into machine code) all come together by "linking". A totally fair question :)

  • It also helps to know a bit about how that machine code relates to a "running program"...

  • ... and how a "running program" uses some bits from the (static) .exe, and other bits from the dynamic runtime (.dll's, or "dynamically linked libraries).

  • All of these details are often completely platform- and OS-specific

  • Hence the (varied) links.

Again, I hope all that helps with your initial question.

paulsm4
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I highly recommend reading John Levine's "Linkers & Loaders". Most of the book is available online here but you should buy the book and support the author. This book taught me quite a lot about how to really dig into the binaries.

D.Shawley
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If you are starting in programming / C++, I will start by having a good understanding of how a static and dynamic libs works and make a couple of tutorials to make a .dll and .lib. Google is your best friend for this: I just find this for e.g: http://www.bogotobogo.com/cplusplus/libraries.php.

Note that the way you make a lib depends on your C++ compiler. The ones I have on top of my head are an integrated development environment (IDE) like Visual Studio or also the gnu C++ compiler.

tiguero
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One point you should know about is ODR, and particularly what it means for inline symbols.

The wikipedia entry may be a good start.

justin
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