Class 24: Building Libraries

Held: Friday, 4 March 2011

Summary: We consider why and how to put C code in separate files.

Related Pages:

• EBoard.
• Lab: Simple Libraries in C.
• Reading: K&R 4.3-4.6.

Notes:

• I did not answer all of last night's questions. Let me know if things are still unclear after the presentation and lab.
• I will be unavailable for much of next week. Please get me questions on the homework before Tuesday's class.
• Assignment 6 is now ready.
• Reading for Sunday night: Unit Testing.
• No CS Extras or CS Table next week!

Overview:

• RPN and Stacks.
• Why We Need Code Libraries.
• Simple Code Libraries in C.
• Lab.

Reverse Polish Notation and Stacks

• We'll run a bit through the K&R example (or at least my variation of it).

Libraries

• We often write functions that we can reuse in other situations and other contexts.
• We could copy those files from program to program.
• But that makes it hard to propagate updates.
• So different languages provide different ways to build libraries or other collections of useful stuff.

• In C, you can break a program into separate files.
• You can compile those files together.
• You can compile those files separately and then link them together.
• There are also ways to build libraries in C.

• How does one compile a file separately?
  • One builds a .o file.
  • make knows about .o files,
• How does one join all the .o files together?
  • With cc.
  • Or with an appropriate make command.

• How does one file know about the code from another file?
  • It can rely on the standard C perspective of If you don't tell me anything about a function, I'll assume that it's available and returns an int.
  • You can explicitly indicate that the function is available.
• Often, we group the information about a library file into a header which we can then include in any file that uses it.
• Headers have a suffix of .h.

Lab

• Do The lab.
• Be prepared to reflect.