This post originates from one quest for using one .lib file in C# project, will hopeful help others on the same path. The mechanics used in different OSes is not exactly the same, so the discuss is divided into two categories.

*nix

A static library usually has one .a extension. When being used in linking process, only the object files used will be linked to the target by default, and this behavior could be turned off by --no-whole-archive. Audience is encouraged to read the manual of ld for this.

A dynamic library usually has the .so (share object) extension. During linking, no actual code and data is copied to the target. Instead, only one slot is created for run time loading.

Windows

The extension for static library is .lib in Windows. Other than the renaming, there’s not much effective difference to my knowledge. The case for dynamic libraries is a bit more complex. Dynamic libraries have .dll (Dynamic Linking Library) extension.

An import library is a library that automates the process of loading and using a dynamic library. On Windows, this is typically done via a small static library (.lib) of the same name as the dynamic library (.dll). The static library is linked into the program at compile time, and then the functionality of the dynamic library can effectively be used as if it were a static library. On Linux, the shared object (.so) file doubles as both a dynamic library and an import library.

Using native code in C sharp project

With the background knowledge on static and dynamic libraries, we are ready to understand the two approaches to this problem.

There are two main types of DLL:

  • Unmanaged DLL (native DLL): used with dllimport in C# project.

  • Managed DLL: using C++/CLI language as the wrapper for native code.

The two approaches are documented in detail at unmanaged and managed. The conclusion drawn by the author seems sensible that unmanaged approach puts the burden on of users of this new DLL, while the managed approach puts the burden on the creator of this new DLL.