Separate Compilation

• We often just want compiler to compile particular portions of our code
  • e.g. confirm code you just wrote is correct
• Frequent compilation can eliminate the issue of fixing all errors at end after finishing implementation problem
• How would we compile separate pieces of source code?
  • If you try to compile without a main function, you get a linking error
  • To compile something without linking, we can specify -c option, e.g. clang -c <file>.c - generates object files
  • object file - contains binary code for compiled code and additional information for linker, e.g. identifiers defined file and what identifiers are required
  • to link object files together, just include all of them in final command for compilation, e.g. clang file1.o file2.o file3.o -o output

Build Automation

• Build process - take source code, produce deployable product
• Build automation - reduction/elimination of manual developer input in favor of automating steps that must be performed
  • ensures consistency on how software is built, allows for quality control to be embedded within the process
  • developers don’t need to remember how to build something
• Modern build automation software can be used to perform tasks such as:
  • downloading and importing new versions of libraries being used
  • automatically retrieving the latest version of the source code e.g. from a git repository
  • running a code analysis tool against the source code to check for suspicious code, formatting etc.
  • running a documentation tool to generate revised documentation
  • building a directory structure containing images, fonts and other resources for the executable to use
  • compiling the code, to one or more targets e.g. iOS and Android
  • running and reporting on automated tests
  • creating an installer so that the program can be easily deployed
• Popular build automation software:
  • Make - very old, for C/C++
  • Ant - implemented in Java
  • Maven - also for Java
  • Gradle - can support C/C++, Scala, Kotlin, offically used for Android
  • Bazel - build automation tool released by Google, part of their internal build tool

Make

• Makefile - textual representation detailing what dependencies exist in our project, how make should compile the program
• Makefiles concist of rules:

target: prerequisites
	recipe

• e.g.

myprogram: main.o vec.o linalg.o
        clang main.o vec.o linalg.o /u2/cs136l/pub/common/cs136.o -o myprogram

vec.o: vec.c vec.h
        clang -c vec.c

linalg.o: linalg.c vec.h linalg.h
        clang -c linalg.c

main.o: main.c vec.h linalg.h /u2/cs136l/pub/common/cs136.h
        clang -c main.c -I/u2/cs136l/pub/common

.PHONY: clean

clean:
        rm *.o myprogram

• Corresponding dependency graph: