Looking at the components of the C library

The C library is not a single library file. It is composed of four main parts that together implement the POSIX functions API:

  • libc: The main C library that contains the well-known POSIX functions such as printf, open, close, read, write, and so on
  • libm: Maths functions such as cos, exp, and log
  • libpthread: All the POSIX thread functions with names beginning with pthread_
  • librt: The real-time extensions to POSIX, including shared memory and asynchronous I/O

The first one, libc, is always linked in but the others have to be explicitly linked with the -l option. The parameter to -l is the library name with lib stripped off. So, for example, a program that calculates a sine function by calling sin() would be ...

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