Compiling Multiple Files in Liux using make

There are generally three distinct steps in compiling some code to and executable. They are:

1.  Compiling the code to Assemble code
2. Assembling the Assembly code to object code
3. linking the object code together into an executable

Example: Consider a project which contains three c programs for e.g. pc1.c pc2.c & pc3.c and a header file test.h which is used in pc2.c . Let the definition of the programs be

pc1.c

#include

int main()

{

      printf("program 1\n");

      return 0;

}

pc2.c

#include

#include"test.h"

void pc2_test()

{

      int i=max;// max is defined in test.h

      printf("%d: value copied from header file\n",i);

      printf("program 2\n");

}

pc3.c

#include

void pc3_test()

{

      printf("program 3\n");

}

test.h

#define max 3

make utility:

make is a system designed to create programs from large source code trees and to maximize the efficiency of doing so. To that effect, make uses a file in each directory called Makefile . This file contains instructions for make on how to build your program and when.

There are three important parts to a Makefile:  the dependency line and the command line and macro line

Procedure:

Step1: Open a file named makefile

>vim makefile

Step1: Defining the dependency line 

fun: pc1.o pc2.o pc3.o                          

Here pc1.o pc2.o pc3.o are the object file for the respective *.c files which defines the project

and fun is the project name

defining the dependencies of pc1.o

pc1.o: pc1.c           

which means main.o is dependent on main.c

if the program is dependent on a external header file

i.e. for the case of pc2.c

pc2.o: pc2.c test.h

Step2: defining the command lines

for the object file to be created the *.c file has to be compiled

 for the  project defnition line 

          gcc -c fun main pc1.o pc2.o pc3.o

compilation line for creating pc1.o etc

           gcc -c pc1.o

The complete program can be sumarized as 

makefile

fun: pc1.o pc2.o pc3.o 

      gcc -c fun main pc1.o pc2.o pc3.o

pc1.o: pc1.c   

      gcc -c pc1.c

pc2.o: pc2.c test.h   

      gcc -c pc2.c

pc3.o: pc3.c   

      gcc -c pc3.c

Step4: To run the makefile

go to the terminal

type make

and to complile the programs

run ./fun  here fun is the project name specified