Any application you write for Linux, whether it be in C or C++, will be linked with the C library, libc. This is so fundamental that you don't even have to tell gcc or g++ to do it because it always links libc. Other libraries that you may want to link with have to be explicitly named through the -l option.
The library code can be linked in two different ways: statically, meaning that all the library functions your application calls and their dependencies are pulled from the library archive and bound into your executable; and dynamically, meaning that references to the library files and functions in those files are generated in the code but the actual linking is done dynamically at runtime.