链接静态库会导致链接库中的错误

Question

I have a small library project that uses OpenGL (glfw and glew). Now, the project compiles fine, but when I create a new project and statically link the library project, VS starts to throw errors in the library project. Why is that?

More specifically, I get this error:

error C1083: Cannot open include file 'GL/glew.h': No such file or directory (file: trenums3d.h)

The project setup is like this: There's the library project 'Foo', which is compiled into a static library ('Foo.lib'). The application project 'Bar' links 'Foo' (I added the folder where Foo.lib resides to Bar's 'Additional Library Directories', as well as the source folder of 'Foo' to Bar's 'Additional Include Directories'). If I compile only the library project, everything works just fine, but compiling the whole solution give me the aforementioned error.

Answer 1

This isn't a proper answer to your question, but just an explanation of the steps required for building an application in a compiled language.

Building a project containing multiple files is a three-step process:

1. Creation and editing of source and header files
2. Compilation of the source files (this step contains many sub-steps ). This step creates object files of all translation units
3. Linking of all object files and libraries to form the final executable

Error like the one shown in your question is emitted in the second step. Linking with libraries happens in a completely different step, and is usually done by a different program than the compiler.

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To answer your question, if linking with a static library also requires linking with the other libraries that the static library depend on, then the answer is normally yes. Static libraries only contain the function in the actual libraries, you can look at a static library more as a collection or archive of object files. Static libraries does not contain any information about other libraries they depend on.

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And as for your problem, with the pre-processor error, it's because you include a header file from your static library, and that header file in turn includes some header files. But the pre-processor doesn't have the secondary included header files in its default search path, so you need to add it.

This still have nothing to do with linking any library, this is a pure pre-processor issue, and is handled in step two in my list above.

Answer 2

I suspect the header files of your static library look like somewhat this:

#ifndef SOMECLASS_H
#define SOMECLASS_H

#include "GL/glew.h"

// ...

#endif

If you include this header file from another library or application, the compiler will open this file and will see that it needs to open GL/glew.h as well in order to be able to "understand" the definition of your class.

This means you need to supply at least the header files of glew. The only way to get rid of this is if you manage to only reference glew files from your .cpp files but not from your .h files. In some cases, forward declarations can be used, but not sure if this will work for glew.

Concerning the linker settings: In case your glew library is built statically as well, you may or may not have to supply that library file and link to it from your project. This depends on how you setup your linker for your own static library. If you have troubles in this step, create a new question.