Intro

Make is, for our purposes, a programming language that facilitates compilation and execution of C++ programs.

Makefiles

A Makefile is both the type and the name of the file that Make executes.

Makefiles can be quite complicated, but in this introduction we’ll confine ourselves to simply writing a basic makefile. A makefile should either be named makefile or Makefile.

Let’s go ahead and create a makefile that we’ll use to compile a short C++ program. First, run

touch makefile

We can divide the makefile into several simple instructions. Let’s define an instruction compile:

compile:
  g++ -c main.cpp

Add another instruction for linking:

link:
  g++ -o main.out main.o

And finally an instruction for executing the program

run:
  ./main.out

It’s convenient to define an instruction that combines all three at once:

all: compile link run

The instruction all executes compile, link and run in the order they appear. The complete makefile will look as follows.

all: compile link run

compile:
  g++ -c main.cpp

link:
  g++ -o main.out main.o

run:
  ./main.out

How to use Make

To run a specific instruction, run

make instruction

In the example makefile above, we could run

make all

which would perform all three instructions compile, link and run. You can naturally also just execute any of them manually.

You can try it out with the C++ program below. Copy it into a file name main.cpp.

#include <iostream>

double f(double x);

int main(int argc, char const *argv[]) {
    double a = 0;
    double b = 1;
    double I = 0;
    int n = 10000;
    double h = (b-a)*1./n;
    for (int i = 0; i < n; i++){
        double x = a + i*h;
        I += f(x);
    }
    I *= h;
    std::cout << "Integral = " << I << std::endl;

    return 0;
}

double f(double x){
    return x*x;
}

Some more advanced usage of make

1. Wildcard. If you have a large number of .cpp that needs to be compiled, you can use the wildcard function of make to compile all files that ends with .cpp. It looks as follows

compile:
  g++ -c $(wildcard *.cpp)

link:
  g++ -o main.out $(wildcard *.o)

The compile instruction compiles all files ending with .cpp while link links all files ending with .o to main.out.