您应该仔细考虑随时间的变化、版本控制、稳定性、兼容性等。

如果有两个应用程序使用共享代码，您是否希望强制这些应用程序一起更改，以防它们需要相互兼容?然后使用dll。所有的exe都将使用相同的代码。

或者你想把它们彼此隔离，这样你就可以改变一个，并确信你没有破坏另一个。然后使用静态库。

DLL地狱是当你可能应该使用一个静态库，但你使用了一个DLL代替，并不是所有的前任都与它兼容。

Static libraries are archives that contain the object code for the library, when linked into an application that code is compiled into the executable. Shared libraries are different in that they aren't compiled into the executable. Instead the dynamic linker searches some directories looking for the library(s) it needs, then loads that into memory. More then one executable can use the same shared library at the same time, thus reducing memory usage and executable size. However, there are then more files to distribute with the executable. You need to make sure that the library is installed onto the uses system somewhere where the linker can find it, static linking eliminates this problem but results in a larger executable file.

其他人已经充分解释了静态库是什么，但我想指出一些使用静态库的注意事项，至少在Windows上:

Singletons: If something needs to be global/static and unique, be very careful about putting it in a static library. If multiple DLLs are linked against that static library they will each get their own copy of the singleton. However, if your application is a single EXE with no custom DLLs, this may not be a problem. Unreferenced code removal: When you link against a static library, only the parts of the static library that are referenced by your DLL/EXE will get linked into your DLL/EXE. For example, if mylib.lib contains a.obj and b.obj and your DLL/EXE only references functions or variables from a.obj, the entirety of b.obj will get discarded by the linker. If b.obj contains global/static objects, their constructors and destructors will not get executed. If those constructors/destructors have side effects, you may be disappointed by their absence. Likewise, if the static library contains special entrypoints you may need to take care that they are actually included. An example of this in embedded programming (okay, not Windows) would be an interrupt handler that is marked as being at a specific address. You also need to mark the interrupt handler as an entrypoint to make sure it doesn't get discarded. Another consequence of this is that a static library may contain object files that are completely unusable due to unresolved references, but it won't cause a linker error until you reference a function or variable from those object files. This may happen long after the library is written. Debug symbols: You may want a separate PDB for each static library, or you may want the debug symbols to be placed in the object files so that they get rolled into the PDB for the DLL/EXE. The Visual C++ documentation explains the necessary options. RTTI: You may end up with multiple type_info objects for the same class if you link a single static library into multiple DLLs. If your program assumes that type_info is "singleton" data and uses &typeid() or type_info::before(), you may get undesirable and surprising results.

Ulrich Drepper关于“如何编写共享库”的论文也是一个很好的资源，详细介绍了如何最好地利用共享库，或者他所说的“动态共享对象”(DSOs)。本文主要讨论ELF二进制格式的共享库，但有些讨论也适用于Windows dll。

静态库必须链接到最终的可执行文件中;它成为可执行文件的一部分，并跟随它到任何地方。每次执行可执行文件时都会加载动态库，并以DLL文件的形式与可执行文件分开。

当您希望能够更改库提供的功能而不必重新链接可执行文件(只需替换DLL文件，而不必替换可执行文件)时，您将使用DLL。

当您没有理由使用动态库时，您可以使用静态库。

c++程序的构建分两个阶段

编译——生成目标代码(.obj) 链接——生成可执行代码(.exe或.dll)

静态库(.lib)只是一个.obj文件的包，因此不是一个完整的程序。它还没有经历构建程序的第二个(链接)阶段。另一方面，dll类似于exe，因此是完整的程序。

如果你构建了一个静态库，它还没有被链接，因此你的静态库的消费者将不得不使用与你使用的相同的编译器(如果你使用g++，他们将不得不使用g++)。

如果相反，您构建了一个dll(并且正确地构建了它)，那么您已经构建了一个所有消费者都可以使用的完整程序，无论他们使用哪种编译器。但是，如果需要跨编译器兼容性，则从dll导出有几个限制。