Basic Introduction of Makefile-set1

What is makefile?

"makefile" is a file which tell to 'make' utility what to do. Most

often, the makefile tells 'make' utility how to compile and link a program.

What is make?

'make' is utility which automatically determines which pieces of a large

program need to be recompiled, and issues commands to recompile them.

Note:

1) to use 'make', you must write a file called the "makefile"

that describes the relationships among files in your program and

provides commands for updating each file. In a program, typically, the

executable file is updated from object files, which are in turn made by

compiling source files.

2) When 'make' recompiles the editor, each changed C source file must be

recompiled. If a header file has changed, each C source file that

includes the header file must be recompiled to be safe. Each

compilation produces an object file corresponding to the source file.

Finally, if any source file has been recompiled, all the object files,

whether newly made or saved from previous compilations, must be linked

together to produce the new executable editor.

Rules to create makefile:

TARGET ... : dependency ...

RECIPE

...

...

TARGET:

A "target" is usually the name of a file that is generated by a

program; examples of targets are executable or object files. A target

can also be the name of an action to carry out, such as 'clean' (*note

Phony Targets::).

Dependency:

A " Dependency" is usually as input that is used as input to create the

target. A target often depends on several files.

RECIPE:

recipe is in a rule with prerequisites and serves to create

a target file if any of the prerequisites change. However, the rule

that specifies a recipe for the target need not have prerequisites. For

example, the rule containing the delete command associated with the

target 'clean' does not have prerequisites.

Simple Example fo makefile:

Here is a straightforward makefile that describes the way an executable

file called 'edit' depends on eight object files which, in turn, depend

on eight C source and three header files.

In this example, all the C files include 'defs.h', but only those

defining editing commands include 'command.h', and only low level files

that change the editor buffer include 'buffer.h'.

edit : main.o kbd.o command.o display.o insert.o search.o files.o \ utils.o
         cc -o edit main.o kbd.o command.o display.o insert.o \ search.o files.o utils.o
main.o : main.c defs.h
             cc -c main.c
kbd.o : kbd.c defs.h command.h
             cc -c kbd.c
command.o : command.c defs.h command.h
                        cc -c command.c
display.o : display.c defs.h buffer.h
                   cc -c display.c
insert.o : insert.c defs.h buffer.h
                cc -c insert.c
search.o : search.c defs.h buffer.h
             cc -c search.c
files.o : files.c defs.h buffer.h command.h
             cc -c files.c
utils.o : utils.c defs.h
             cc -c utils.c
 clean :
            rm edit main.o kbd.o command.o display.o \
                insert.o search.o files.o utils.o

We split each long line into two lines using backslash/newline; this is

like using one long line, but is easier to read. *Note Splitting Long

Lines: Splitting Lines.

To use this makefile to create the executable file called 'edit',

type:

     make

To use this makefile to delete the executable file and all the object

files from the directory, type:

     make clean

To execute the executable file:

./edit