• Compilers
• Make/Makefiles

Compilers are programs that

• convert program source code to executable form
• "executable" might be machine code or bytecode

• applies source-to-source transformation (pre-processor)
• compiles source code to produce object files
• links object files and libraries to produce executables

clang is an alternative C compiler  (also available in CSE)

Note that dcc and 3c are wrappers around gcc/clang

• providing more checking and more detailed/understandable error messages
• better run-time support (e.g. array bounds, use of dynamic memory)

Stages in C compilation:  pre-processing, compilation, linking

When multiple C files are involved:

Compilation/linking with gcc

gcc -c Stack.c
produces Stack.o, from Stack.c and Stack.h
gcc -c bracket.c
produces bracket.o, from bracket.c and Stack.h
gcc -o rbt bracket.o Stack.o
links bracket.o, Stack.o and libraries
producing executable program called rbt

Note that stdio,assert included implicitly.

gcc is a multi-purpose tool

• compiles (-c), links, makes executables (-o)

Compilation process is complex for large systems.

How much to compile?

• ideally, what's changed since last compile
• practically, recompile everything, to be sure

• programmers to document dependencies in code
• minimal re-compilation, based on dependencies

Example multi-module program …

make is driven by dependencies given in a Makefile

A dependency specifies

target : source1 source2 …
        commands to build target from sources

e.g.

game : main.o graphics.o world.o
	gcc -o game main.o graphics.o world.o

Rule: target is rebuilt if older than any source_i   (applied recursively)

game : main.o  graphics.o  world.o
	gcc -o game main.o graphics.o world.o

main.o : main.c graphics.h world.h
	gcc -Wall -Werror -c main.c

graphics.o : graphics.c world.h 
	gcc -Wall -Werror -c graphics.c

world.o : world.c
	gcc -Wall -Werror -c world.c

If make arguments are targets, build just those targets:

prompt$ make world.o
gcc -Wall -Werror -c world.c

If no args, build first target in the Makefile.

prompt$ make
gcc -Wall -Werror -c main.c
gcc -Wall -Werror -c graphics.c
gcc -Wall -Werror -c world.c
gcc -o game main.o graphics.o world.o

Makefiles can contain "variables"

• e.g. CC,  CFLAGS,  LDFLAGS
• can easily change which C compiler used, etc

Stack.o : Stack.c Stack.h

as

Stack.o : Stack.c Stack.h
        $(CC) $(CFLAGS) -c Stack.c