共享库（.so）文件是否需要在链接时显示（或指定）？

Question

Do shared libraries (.so) files need to present (or specified) at link time?

I've read here ( Difference between shared objects (.so), static libraries (.a), and DLL's (.so)? ) that .so files must be present at compile time, but in my experience this is not true?

Doesn't shared libraries just get linked at runtime using dlopen and dlsym , so that the library may not be present on the system, when the application is linked?

Answer 1

Most shared libraries need to be present both at build time and at run time. Notice that shared libraries are not DLL s (which is a Windows thing).

I assume you code for Linux. Details are different on other OSes (and they matter).

For example, if you are compiling a Qt application, you need the Qt shared libraries (such as /usr/lib/x86_64-linux-gnu/libQt5Gui.so and many others) both when building your application and when running it. Read about the dynamic linker ld-linux.so(8) & about ELF .

But you are asking about dynamic loading (using dlopen(3) with dlsym(3) ...) of plugins . Then read Levine's Linkers & Loaders , Program Library HowTo , C++ dlopen mini HowTo , and Drepper's How To Write Shared Libraries

See also this answer .

Some libraries and frameworks try to abstract the loading of plugins in an OS-neutral manner. Read eg about Qt plugins support, or about POCO shared libraries (poorly named, it is about plugins).

Answer 2

You can have it both way, it all works.

While with library present at compile time,instead of get library by dlopen/LoadLibrary explictly, you can use all the functions directly