2.4.7. Static and dynamic libraries with GCC

Combining static and dynamic linking balances portability and efficiency. The GNU Compiler Collection (GCC) automatically selects shared objects over static archives unless you configure it otherwise. That resolution order determines which library versions to link and which linker options apply.

Static libraries are packaged as libname.a archive files. Dynamic libraries are packaged as libname.so shared objects. Together, those are the two shapes gcc must choose between when both linking modes are available for the same library name.

For each -lfoo option, gcc searches the library directories (including paths from -Lpath) for libfoo.so first and libfoo.a second. Depending on what gcc finds on the search path, linking proceeds in one of these ways:

Because of these rules, the best way to select the static or dynamic version of a library for linking is having only that version found by gcc. This can be controlled to some extent by using or leaving out directories containing the library versions, when specifying the -Lpath options.

Additionally, because dynamic linking is the default, the only situation where linking must be explicitly specified is when a library with both versions present should be linked statically. There are two possible resolutions: specifying the static libraries by file path instead of the -l option, or using the -Wl option to pass options to the linker.