kỹ thuật điện hệ điều hành os + thí nghiệm 3 en sinhvienzone com

Motivation cont. Problems  Long files are harder to manage for both programmers and machines  Every change requires long compilation  Many programmers can not modify the same file

Makefile Utility

 Small program

 Single file

 “Not so small” programs

 Many lines of code

 Multiple components

 More than one programmer

Motivation (cont.)

 Problems

 Long files are harder to manage (for both programmers and

machines)

 Every change requires long compilation

 Many programmers can not modify the same file

simultaneously

Division to components is desired

Program Compiling

 Manual

 Efforts

 Shell script

 Time

 Makefile

 Convenient

 Compiling time

 Text file

 make

 *NIX systems

 Build, install, and uninstall programs

 Avoid re-building targets which are up-to-date

 Not limited to C/C++ programs

Project:

main.c, sum.c, sum.h

sum.h is included in main.c & sum.c

 executable file: sum

Example (cont.)

 Compile

$ gcc –o sum main.c sum.c

or

$ gcc –c main.c

$ gcc –c sum.c

$ gcc –o sum main.o sum.o

=> What happens if file main.c is modified

Project Structure

sum.c sum.h main.c

sum.o main.o

sum

Makefile content

# This is an example of Makefile

CC=gcc

sum: main.o sum.o

$(CC) –o sum main.o sum.o main.o: main.c sum.h

$(CC) –c main.c sum.o: sum.c sum.h

$(CC) –c sum.c Rule TAB

Target Dependency Action

Built-in Macros

sum: main.o sum.o

gcc –o $@ $^

.c.o:

gcc –c $<

main.o sum.o: sum.h

gcc –c $*.c

Built-in Macros (cont.)

$@ - The name of the target of the rule

$< - The name of the first dependency

$^ - The names of all the dependencies

$? - The names of all dependencies that are newer

than the target

$* - The name of the target of the rule without

extension

Make Operation

 Project dependencies tree is constructed

 Target of first rule should be created

 We go down the tree to see if there is a target that should

be recreated This is the case when the target file is older than one of its dependencies

 In this case we recreate the target file according to the

action specified, on our way up the tree Consequently,

more files may need to be recreated

 If something is changed, linking is usually necessary

Make Operation (cont.)

File Last Modified

sum 10:03

main.o 09:56

main.c 10:45

Make Operation (cont.)

sum.o main.o

sum

10:03

Make Operation (cont.)

 Operations performed:

gcc –c main.c gcc –o sum main.o sum.o

 main.o should be recompiled (main.c is newer).

 Consequently, main.o is newer than sum and therefore sum

should be recreated (by re-linking)

Questions???