Makefile

Special Thanks to Dr. Pinchas Weisberg :smiley:

Create a file by the name of makefile or Makefile in the following format

target: prerequisites
[TAB] command

for example

myprog: myprog.cpp myprog.h
  g++ -o myprog myprog.cpp
clean:
  rm myprog

The make updates a target e.g myprog that depends on prerequisite files myprog.cpp myprog.h if any of the prerequisite files have been modified or the target doesn't exist.

Rules of a makefile

• By default, make starts with the first target, thus make with no arguments , reads the makefile in the current directory and processes the first rule

• But before make can process this rule, it must check if the prerequisite files depend on other files, and process the rules for them

• If some other rule is not depended on by the goal, that rule is not processed, unless you tell make to do so, e.g. make clean

Another example

sum: main.o sum.o
  g++ –o sum main.o sum.o

main.o: main.cpp sum.h
  g++ –c main.cpp

sum.o: sum.cpp sum.h
  g++ –c sum.cpp

clean:
  rm sum main.o sum.o

Here the makefile will start with the target sum. Since sum is dependent on main.o and sum.o it will go to them first.

The target main.o will check for main.cpp and sum.h. Afterward it will run g++ –c main.cpp and compile main.o

The clean target isn't dependent on sum and if we were to run it we will type in make clean

Makefile Variables

To clean up our code we can use variabeles. To delcare a variable type var_name = my_var and to use them just use the dollar sign $(var_name).

For example:

OBJFILES = main.o sum.o
PROGRAM = sum
CC = g++
CFLAGS = -g -std=c++11 –Wall

$(PROGRAM): $(OBJFILES)
  $(CC) $(CFLAGS) -o $(PROGRAM) $(OBJFILES)

clean:
  rm $(PROGRAM) $(OBJFILES)

Here we declared and used 4 different variables: OBJFILES, PROGRAM, CC and CFLAGS.

Exercise

Create a makefile for the following files: main.cpp, Point.cpp, Point.hpp, Rectangle.cpp, Rectangle.hpp, Circle.cpp Circle.hpp, Triangle.cpp Triangle.hpp. Rectangle, Circle and Triangle are all dependent on Point

Solution

Special Symbols

Let say we have the following makefile

all: library.cpp main.cpp

• $@ evaluates to all

• $< evaluates to library.cpp

• $^ evaluates to library.cpp main.cpp

Example 1: Naive

CC=gcc
CFLAGS=-I.
DEPS = hellomake.h

%.o: %.c $(DEPS)
    $(CC) -c -o $@ $< $(CFLAGS)

hellomake: hellomake.o hellofunc.o 
    $(CC) -o hellomake hellomake.o hellofunc.o

The -I. is included so that gcc will look in the current directory (.) for the header files. More examples can be found here.

Let explain the following rule

%.o: %.c $(DEPS)

The rule says that the .o file depends upon the .c version of the file and the .h files included in the DEPS macro. The rule then says that to generate the .o file, make needs to compile the .c file using the compiler defined in the CC macro.

$(CC) -c -o $@ $< $(CFLAGS)

The -c flag says to generate the object file. the -o stands for output and -o $@ says to put the output of the compilation in the file named on the left side of the : e.g. hellomake The $< is the first item in the dependencies list

Bash and Makefiles

Lets say that we only have main.cpp, makefile and a s.sh

makefile

a.out : main.cpp Point.cpp Point.hpp
    g++ -o $@ $^

main.cpp

#include "Point.hpp"

#include <iostream>
using namespace std;

int main() {
    Point p1;
    cout << "p1 = " << p1.to_string() << endl;

    p1.setX(10);
    p1.setY(20);
    cout << "p1 = " << p1.to_string() << endl;

    Point p2 {11,21};
    cout << "p2 = " << p2.to_string() << endl;
    return 0;
}

s.sh

wget -O Point.hpp https://raw.githubusercontent.com/erelsgl-at-ariel/cpp-5780/master/02-classes-constructors-destructors/4-constructors/Point.hpp && \
wget -O Point.cpp https://raw.githubusercontent.com/erelsgl-at-ariel/cpp-5780/master/02-classes-constructors-destructors/4-constructors/Point.cpp && \
make && \
echo -e "===Archiving and Compressing===\n" 
tar cvzf files.tar.gz *.cpp *.hpp *.out

mkdir program_dir && \
echo -e "===Moving files===\n" && \
mv files.tar.gz program_dir 

echo -e "===starting program===\n"
./a.out

# alias gfast="git add *.cpp *.hpp makefile *.md && git commit -m \"fast commit\" && git push"
gfast