Introduction. Introduction to gcc and Makefiles. Stef Nychka. September 21, Department of Computing Science University of Alberta

Transcription

1 1 / 11 Introduction Introduction to gcc and Makefiles Stef Nychka Department of Computing Science University of Alberta September 21, 2007

2 2 / 11 Overview Overview Sample Files gcc Object Files and Executables Linking Libraries Useful Compilation Flags Better to Use Makefiles Makefiles Makefile Rules clean Rule and Comments Makefile Guidelines Invoking Your Makefile

3 3 / 11 Download Sample Files Your TA will use sample files to illustrate concepts, and you can follow along. To get these files 1. Create a directory called make_eg 2. Go to Resources page 3. Download make_eg.tar.gz to make_eg 4. cd to make_eg, then extract files from make_eg.tar.gz 5. Go to Assignment 1 page 6. Download filter, sketchpad, libmove.a, move.h to make_eg If using Bon Echo, remove.htm from filter and sketchpad 7. Make filter and sketchpad executable.

4 4 / 11 -c and -o You will use gcc to compile your C code. (Below and on other slides, TA will run commands on files from make_eg.tar.gz... please follow along) gcc -c draw0.c Compiles draw0.c, creating an object file (machine code) whose default name will be draw0.o. gcc -o draw0 draw0.o -L. -lm -lmove No -c means linking is now done, which results in an executable. draw0.o and any code from library files are linked. -o specifies that the executable will be called draw0.

5 5 / 11 -l and -L C libraries contain compiled code. To use the functions like sin from the math library, include math.h. To use functions like rotate_point from the move library, include move.h. (TA will show includes in draw0.h). You need to link to these libraries manually. -lname corresponds to a file named libname.a: gcc -o draw0 draw0.o -L. -lm -lmove -lm links the standard library math (/usr/lib/libm.a) -lmove links the local library move (./libmove.a) -L. tells gcc to look in current directory for libraries The math library is the only standard library you will need to manually link for Assignment 1.

6 6 / 11 -Wall and -ansi gcc -Wall -ansi -c draw0.c -Wall enables all (well, most) warnings, which often catch bugs. -ansi ensures your code conforms to the 1990 C ANSI standard that your text book uses. In 201, you need to always use these flags.

7 7 / 11 Better to Use Makefiles You could type gcc commands at the command prompt, but it s better to put these commands into a Makefile. Makefiles automate compilation. This is less error prone. This allows others to compile your code without understanding how to compile your code. It only compiles what needs to be compiled, which saves time for programs with many source files. Note a Makefile is just a text file.

8 8 / 11 Makefile Rules The main construct in a Makefile is a rule: target : prerequisites <TAB>command1 example: draw0.o: draw0.c draw0.h gcc -Wall -ansi -c draw0.c If prerequisites, draw0.c or draw0.h, are newer than the target, then must create a new target, draw0.o. How? Run the command gcc. There has to be a tab character before each command

9 9 / 11 clean Rule and Comments You are required to have a clean rule to remove.o files, your executable and core files: clean: -rm -f *.o draw0 core Because clean is not a file and there are no prerequisites, it is called a phony rule. The - in front of rm allows any further actions to take place if rm generates an error Comments start with a #, and continue to the end of the line: # This is a comment

10 10 / 11 Guidlines for Writing an Assignment 1 Makefile Using Makefile (from make_eg.tar.gz) TA will show: the first rule has the executable as the target, and all.o files as a prerequisites; a prerequisite that is also a target (e.g. draw0.o) causes the rule where it s a target to be invoked first; that each.c file should be a prerequisite once, with its corresponding.o file as the target; prerequisites also contain.h files whose.c files are in your directory (but not C standard library.h files). Start with the sample Makefile at the Makefiles Tutorial: Resources Makefiles

11 11 / 11 Invoking Your Makefile TA will show you how to do this: Can invoke an individual target by typing make <target>. You have to do this for all phony rules. e.g. type make clean. Invoke the first rule by typing make. It should create the executable. More advanced Makefile concepts online at the tutorial. You can read this on your own.