Menu
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?
988
Shared libraries (also called dynamic libraries) are linked into the program in two stages. First, during compile time, the linker verifies that all the symbols (again, functions, variables and the like) required by the program, are either linked into the program, or in one of its shared libraries.
Shared libraries are the most common way to manage dependencies on Linux systems. These shared resources are loaded into memory before the application starts, and when several processes require the same library, it will be loaded only once on the system. This feature saves on memory usage by the application.
A file with the . SO file extension is a Shared Library file. They contain information that can be used by one or more programs to offload resources so that the application(s) calling the SO file doesn't have to actually provide the file.
Most shared libraries need to be present both at build time and at run time. Notice that shared libraries are not DLLs (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 e.g. about Qt plugins support, or about POCO shared libraries (poorly named, it is about plugins).
79
If you love us? You can donate to us via Paypal or buy me a coffee so we can maintain and grow! Thank you!
Donate Us With
