Slide 1staticFunction static dataThe compilation processCompiling large programsDependenciesmakeMakefile rule syntaxRunning makeRules with no sourcesRules with no commandsVariablesMore variablesSpecial variables includeAuto-conversionsDependency generationMidterm grades vs. initial experienceQuestions?David Notkin Autumn 2009 CSE303 Lecture 20staticmakestatic// example.cint passcode = 12345; // publicstatic int admin_passcode = 67890; // private•static used on global variables and functions–visible only to the current file/module (sort of like Java's private)–declare things static if you do not want them exposed–avoids potential conflicts with multiple modules that happen to declare global variables with the same names–passcode will be visible through the rest of example.c, but not to any other modules/files compiled with example.cCSE303 Au09 2Function static data•When used inside a functionstatic type name = value;… declares a static local variable that will be remembered across callsint nextSquare() { static int n = 0; static int increment = 1; n += increment; increment += 2; return n;}•nextSquare() returns 1, then 4, then 9, then 16, ...CSE303 Au09 3The compilation process•What happens when you compile a Java program?$ javac Example.java–Example.java is compiled to create Example.class•But...–what if you compile it again?–what if Example.java uses Point objects from Point.java?–what if Point.java is changed but not recompiled, and then we try to recompile Example.java?Compiling large programs•Compiling multi-file programs repeatedly is cumbersome$ gcc -g -Wall -o myprogram file1.c file2.c file3.c•Retyping the above command is wasteful–for the developer (so much typing), and it’s error-prone–for the compiler (may not need to recompile all; save them as .o)•Improvements–use up-arrow or history to re-type compilation command for you–use an alias or shell script to recompile everything–use a system for compilation/build management, such as makeDependencies•Dependency : When a file relies on the contents of another – can be displayed as a dependency graph–to build main.o, we need data.h, main.c, and io.h–if any of those files is updated, we must rebuild main.o–if main.o is updated, we must update project1 (which is probably an executable like a.out)make•make : a utility for automatically compiling ("building") executables and libraries from source code.–a very basic compilation manager–often used for C programs, but not language-specific–primitive, but still widely used due to familiarity, simplicity–similar programs: ant, maven, IDEs (Eclipse), ...•makefile : A script file that defines rules for what must be compiled and how to compile it.–makefiles describe which files depend on which others, and how to create / compile / build / update each file in the system as needed.–The basic idea is to compare file modification dates and to rebuild any file A dependent on another file B that has changed more recently than AMakefile rule syntaxtarget: source1 source2 ... sourceN command command ...Example:myprogram: file1.c file2.c file3.cgcc -o myprogram file1.c file2.c file3.c•The command line must be indented by a single tab•not by spaces; NOT BY SPACES! SPACES WILL NOT WORK!Running make$ make target•uses the file named Makefile in current directory•finds rule in Makefile for building target–if the target file does not exist, or if it is older than any of its sources, its commands will be executed•variations:$ make–builds the first target in the Makefile$ make -f makefilename$ make -f makefilename target–uses a makefile other than MakefileRules with no sourcesclean: rm file1.o file2.o file3.o myprog•make assumes that a rule's command will build or create its target–but if your rule does not actually create its target, the target will still not exist the next time, so the rule will always execute (clean above)–make clean is a convention for removing all compiled files (but not source or header files!)Rules with no commandsall: myprog myprog2myprog: file1.o file2.o file3.o gcc -g -Wall -o myprog file1.o file2.o file3.omyprog2: file4.c gcc -g -Wall -o myprog2 file4.c...•all rule has no commands, but depends on myprog and myprog2–make all ensures that myprog, myprog2 are up to date–all rule often put first, so that typing make will build everythingVariablesNAME = value (declare)$(NAME) (use)OBJFILES = file1.o file2.o file3.oPROGRAM = myprog$(PROGRAM): $(OBJFILES) gcc -g -Wall -o $(PROGRAM) $(OBJFILES)clean: rm $(OBJFILES) $(PROGRAM)•variables make it easier to change one option throughout the file–also makes the makefile more reusable for another projectMore variablesOBJFILES = file1.o file2.o file3.oPROGRAM = myprogifdef WINDIR # assume it's a Windows box PROGRAM = myprog.exeendifCC = gccCCFLAGS = -g -Wall$(PROGRAM): $(OBJFILES) $(CC) $(CCFLAGS) -o $(PROGRAM) $(OBJFILES)•variables can be conditional (ifdef above)•many makefiles create variables for the compiler, flags, etc.–this can be overkill, but you will see it "out there"Special variables include$@ the current target file$^ all sources listed for the current target$< the first (left-most) source for the current targetmyprog: file1.o file2.o file3.o gcc $(CCFLAGS) -o $@ $^file1.o: file1.c file1.h file2.h gcc $(CCFLAGS) -c $<Auto-conversions•Rather than specifying individually how to convert every .c file into its corresponding .o file, you can set up an implicit target:# conversion from .c to .o.c.o: gcc $(CCFLAGS) -c $<–"To create filename.o from filename.c, run gcc -g -Wall -c filename.c"•For making an executable (no extension), simply write .c :.c: gcc $(CCFLAGS) -o $@ $<•Related rule: .SUFFIXES (what extensions can be used)Dependency generation•You can make gcc figure out dependencies for you:$ gcc -M filename–instead of compiling, outputs a list of dependencies for the given file$ gcc -MM filename–similar to -M, but omits any internal system libraries (preferred)•Example:$ gcc -MM linkedlist.clinkedlist.o: linkedlist.c linkedlist.h util.h•related command: makedependMidterm grades vs. initial experience•Unix experience–49% None–37% A little –11% Quite a bit–3% Pays my tuition•C/C++ experience–52% None–37% A little –9%
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