CS465 - Unix

C Programming (cc/make and

configuration control)

Unix C compilers

• Most Unix system have a C compiler built-in. Both the cc and the gcc utilities compile and link C source code.

• Syntax:$ cc [options] source(s) [-o exefile] $ gcc [options] source(s) [-o exefile]

(depending on system)

• If -o is not used, by default the executable filename is a.out.

• To run the program, simply type the name of the executable file (default: a.out).

cc Example (using a.out)

$ cat world.c#include <stdio.h>main (){ printf ("Hello World!");}$ cc world.c$ a.outHello World!$

gcc Example (using named exe)

$ gcc world.c -o world.exe$ world.exeHello World!$

• Place function main() in one source code (.c) file

• Place each C function (or set of C functions) into a separate source code (.c) files

• Example: Compile and link the code in prog1.c and prog2.c into the executable file prog.

$ cc prog1.c prog2.c -o prog

Compiling with Multiple Source Files

• If you compile each source file separately, it can be used by whatever program needs it.

– The compiler -c option allows separate compilation of files, creating object code, not executable code.

• Create a header (.h) file for each function file that will be compiler separately.

• Add:

#include "f1.h"

lines to each file that calls a function from another file.

Separate Compilation of Multiple Source Files (1)

• Compile each source code file separately into a compiled object file:

$ cc –c f1.c$ cc –c f2.c$ cc –c main.c

• Link the object files together with the main program object file into an executable file:

$ cc f1.o f2.o main.o –o exename

• Avoids rewriting similar code for each project

Separate Compilation of Multiple Source Files (2)

• Linking the object files together

– Resolves relative addresses of:

• variables

• functions

– Creates a single Executable file

Object File Linking

• Write a useful set of Math Functions and put them in the source file math.c

• Create a header file math.h

• Compile math.c into an Object File

$ cc –c math.c

• The -c option creates object code file math.o by default

Can use –o file.o to save under a different name.

Example

• Now suppose file mainfile.c uses the functions in math.c

– Add the line #include "math.h" to mainfile.c

– Compile mainfile.c into an Object File

$ cc –c mainfile.c

• Link the two together and create executable, myprog

$ cc mainfile.o math.o -o myprog

• Run using the executable name:

$ myprog

Example (cont)

• OR can compile and link in One Step:

$ cc mainfile.c math.o -o myprog

• And then run:

$ myprog

Example (variation)

What is make?

• The make command automates the process of building files that depend on other files.

• Typically used for program development:

– runs the compiler only when necessary

– uses file access times to decide when it is necessary

• However, make can be used for lots of tasks (not just for programming).

What is a Dependency?

• Say that file foo should be rebuilt whenever file blah is changed.

– If blah is newer than foo, we need to rebuild foo .

– Therefore foo depends on blah

From our compiler example:• myprog is built from mainfile.o and math.o• mainfile.o is built from mainfile.c• math.o is built from math.c• Dependency Graph: myprog

math.o mainfile.o

mainfile.cmath.c

Program Dependencies

• Change in math.c causes:– math.o Outdated– myprog Outdated

• But there would be no need to recompile mainfile.c

• Use make to determine recompilation requirements!

NAME make - utility to maintain groups of programs

DESCRIPTIONThe purpose of the make utility is to determine automatically which pieces of a large program need to be recompiled, and issue the commands to recompile them.

make manpage

Makefiles• make needs a list of rules on how to create the final

target file. Rules include:

– file dependencies

– instructions on how to build the dependent file

• The rules are located in file:

– Default file: makefile

– You can also use: $ make –f filename

Rules Format

target : dependencies

command1

:

commandn

target depends on the files listed after the colon.

commands are Unix commands that build a new target file.

These M

UST be tabs!!

!

Simple Rule Example

• This rule would tell make that the file linecount depends on the file foo.c:

linecount : foo.c

wc –l foo.c > linecount

• Rule says that to build the file linecount, the command “wc –l foo.c > linecount” should be run.

prog.exe: getio.c anal.c cc getio.c anal.c –o prog.exe

getio.c: numsin.c wordsin.ccat numsin.c wordsin.c > getio.c

anal.c: stats.c avg.ccat avg.c stats.c > anal.c

Sample Makefile #1File anal.c is built by concatonating stats.c and avg.c. File getio.c is built by concatonating numsin.c and wordsin.c. The executable is then built by compiling and linking anal.c and getio.c.

myprog: main.o f1.o f2.o cc -o myprog main.o f1.o f2.o

main.o: main.c f1.h cc -c main.c

f1.o: f1.c f1.h f2.h cc -c f1.c

f2.o: f1.c f2.h cc -c f2.c

Sample Makefile #2

Given that function main calls function f1, and function f1 calls function f2. (i.e. f1 is dependent on f2, and main is dependent only on f1):

myprog: main.o f1.o f2.o

cc -o myprog main.o f1.o f2.o

• This is a Rule:

target dependencies

• make checks to see if all files are up-to-date

If myprog is newer than all others, make assumes everything is up-to-date

If everything is up-to-date, does nothing

• Otherwise make searches the rule for dependencies

Makefile Rules

myprog: main.o f1.o f2.o

cc -o myprog main.o f1.o f2.o

target dependencies

•Rebuilds out of date dependencies or sub-dependencies according to other rules in the Makefile

•After all Dependencies are up-to-date the shell command on Second Line is executed

• NOTE: Commands must be preceded by a TAB --- NO SPACES!!!

Makefile Rules (cont)

$ make [-f makefile]

-f use makefile for rules

Other Flags:-n simulate compilation actions

(show actions, but don’t do them)-k ignore errors

make syntax

Example of Running make

$ cat testmaketest1: test1.c cc test1.c -o test1$ make -f testmakecc test1.c -o test1$ test1Enter positive whole base: 3Enter positive whole exponent: 3

Base 3 to the 3 power = 27$

Configuration Control

• Protects and controls access to files so that more than one person is not editing the same file at the same time.

• Often used when multiple people are working on the same source code file of a program

• Can also be used for any other file that multiple people have access to.

Configuration Control Programs

• Two most popular:

– RCS - revision control system

– SCCS - source code control system

• Our textbook covers SCCS

• Unix in Nutshell covers RCS

What Configuration Control programs provide

A collection of tools that lets you:

• Put files under configuration control

• Check out one modifiable copy

• Put write locks on updates

• Check out multiple read-only copies

• Check in and document changes

• Print histories

• Merge updates