What is the difference between .o, .a, and .so files?

Question

I know .o are object files, .a are static libraries and .so are dynamic libraries? What is their physical significance? When can I use som

Answer 1

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 user's system somewhere where the linker can find it, static linking eliminates this problem but results in a larger executable file.