Libraries

A library is code enclosed in external binary files, which contains functionality to be included in a different programme. With a focus on the C programming language, the source code can be a compilaion target for:

• Static library
• Dynamic library
• Executable

.a - Static Library

An archive .a file contains a library that may contain few functions or include an entire library of functions. Archive files are typically created by the GNU ar utility. They are used as a compilation artifact and consequently embedded inside the target binary. The final binary that get produced from this libraries does not depend on the .a to work.

.so - Shared Object | Dynamic Library

A shared object .so file is a shared library used by programs. It contains common programme functions and logic that multiple programs require access to, .so files allow programs to access common functions from one shared place in a computer's system memory, rather than implementing their own versions of the functions. They must be present in the system and reachable from the linked ld.

Dynamic libraries are loaded at runtime, which means that they are not linked into a program at compile time like static libraries.

What's inside a library files

To view a list of the functions an .so file contains, use:

nm objectfile.o
nm -D path/to/filename.so

To understand the dynamic libraries that an executable requires you can run:

ldd </path/to/executable>

Which will print all shared object dependencies.

Where are the libraries?

Libraries manageg by package managerts are usually installed at LD_LIBRARY_PATH. To see it:

echo $LD_LIBRARY_PATH

Often resulting into the following directories:

• /lib
• /usr/lib
• /usr/local/lib

While to add locations execute:

export LD_LIBRARY_PATH="/path/to/your/nanaged/library/directory:$LD_LIBRARY_PATH"