1. makefiles

2. makefiles
Problem: You are working on one part of a large programming project (e. g., MS Word).
It consists of hundreds of individual .c files all linked together to form winword.exe.
You make a change to one of these .c files and now need to rebuild word.exe.
How do you do it without having to recompile hundreds of .c files that haven’t changed?

3. w/out makefiles g++ -o word.exe f1.c f2.c f3.c f4.c … f999.c
But only f4.c has changed and only needs to be recompiled!
Compiler option to create intermediate (object modules) files:
g++ -c f1.c
g++ -c f2.c …
g++ -c f999.c
g++ -o word.exe f1.o f2.o f3.o … f999.o
Then I just manually do: g++ -c f4.c then relink.

4. But how can I automatically determine only what needs to be recompiled?
Write a program that looks at the modification time of the .c file and the .o (or .exe) file. If the mod time of the .c file is more recent than the mod time of the .o (or .exe) file, then we know that we know that we need to recompile and relink.
But I don’t want to write this program!

5. makefiles Consist of: Definitions (like constants):
Comments (begin with #)
Definitions
Dependencies
Commands
Definitions (like constants):
CC = g++ -g Or
CC = g++ -O3 …
To use these definitions we evaluate $(CC)

6. Dependency a:<tab>b c d …
Means that a is dependent upon (needs) b and c and d …
What is word.exe dependent upon?
g++ -o word.exe f1.o f2.o f3.o … f999.o
word.exe is dependent upon f1.o, f2.o, …, f999.o
word.exe: f1.o f2.o … f999.o
What is f1.o dependent upon?

7. Dependency & command
Usually, a dependency is followed by a command to rebuild/recreate/update the entity to the left of the colon (called a tag).
Dependencies are hierarchical.
word.exe:<tab> f1.o f2.o … f999.o
<tabs> g++ -o word.exe f1.o f2.o … f999.o
f1.o:<tab> f1.c
<tabs> g++ -c f1.c
f2.o:<tab> f2.c
<tabs> g++ -c f2.c …

8. Example (including definitions and comments)
#for debug version:
CC = g++ -g
#for production version:
#CC = g++ -O3
word.exe:<tab> f1.o f2.o … f999.o
<tabs> $(CC) -o word.exe f1.o f2.o … f999.o
f1.o:<tab> f1.c
<tabs> $(CC) -c f1.c …

9. Example (more than 1 command)
#for debug version:
CC = g++ -g
word.exe: f1.o f2.o … f999.o
echo link word.exe
$(CC) -o word.exe f1.o f2.o … f999.o
f1.o: f1.c
echo compile f1.c
$(CC) -c f1.c …

10. Example (make more than one)
#for debug version:
CC = g++ -g
all: word.exe fred.exe …
word.exe: f1.o f2.o … f999.o
echo link word.exe
$(CC) -o word.exe f1.o f2.o … f999.o
f1.o: f1.c
echo compile f1.c
$(CC) -c f1.c …

11. make make all make word.exe make f1.o make fred.exe
Checks the first dependency that appears in the file makefile.
make all
Checks the all dependency in makefile.
make word.exe
make f1.o
make fred.exe
make –f myMakeFile all
Checks the all dependency in file myMakeFile.

12. Assignment
Create a file called f1.cpp. It should contain the following function:
int squareIt ( int x ) {
//insert code to calc and return the square of x }
Create a file called f2.cpp. It should contain the following function:
int cubeIt ( int x ) {
//insert code to calc and return the cube of x

13. Assignment (cont’d.)
3. Create a main program in a file called main.cpp
#include <stdio.h>
extern int squareIt ( int x );
extern int cubeIt ( int x );
int main ( int argc, char* argv[] ) { … }

14. Assignment (cont’d.)
Main should ask the user to enter a number. Main should then call the two functions, add up the values, and then print out this sum.
Main should repeat the above 3 times.
Get this to compile, link, and run.

15. Assignment (cont’d.)
Then create a makefile which should only recompile and relink only when changes are made.
The makefile should also contain a tag called clean. Whenever the user types make clean, this tag should simply delete all .o and .exe files. See the man page for rm. If no .o or .exe files are present, make clean should not report any errors.

16. Assignment (cont’d.)
Document each file and each function with doxygen.