How to write a Makefile

Assume there are more number of source files to be compiled using a set of commands everytime is a tedious process. So there is a facility to compile everything at a stretch is by the use of a Makefile.

The makefile can be named as either “Makefile” or “makefile”.

Let me define four files for my simple application, create a new directory and store all the files given below

• main.c  (which contains the main program)


• sum.c (summing function is defined)


• hello.c (print hello world)


• function.h (function prototypes are declared)

You can download all the files here

//function.h

int sum(int,int);
void print_hello();

//hello.c

#include <stdio.h>
#include "function.h"
void print_hello()
{
printf("Hello World \n");
}

//sum.c

#include "function.h"
int sum(int a, int b)
{
int c;
c=a+b;
return c;
}

//main.c

#include <stdio.h>
#include "function.h"
int main()
{
int a=10,b=20,c;
print_hello();
c=sum(a,b);
printf("The sum of two numbers is %d ",c);
return 0;
}

There are different methods of compiling this file

Method 1: (gcc command based)

gcc main.c sum.c hello.c –o pradeep

once you execute the above command, an executable named pradeep is created and you can see the output by typing ./pradeep

Method 2: using Makefile

The basic makefile is composed of:

This syntax applied to example would look like:

target: dependencies

[tab] system command

all:

gcc main.c sum.c hello.c –o pradeep

to run this make file(the file name should be Makefile or makefile), execute the command

make

Method 3: using Makefile with dependencies

There may be a chance of using different targets in your makefile, this is because if you modify a single file in your project, you don't have to recompile everything, only what you modified.
Here is an example

all: pradeep

hello: main.o sum.o hello.o
gcc main.o sum.o hello.o -o hello

main.o: main.c
gcc –c main.c

sum.o: sum.c
gcc –c sum.c

hello.o: hello.c
gcc –c hello.c



Method 4: using variables

CC=gcc
CFLAGS=-c -Wall

all: hello

hello: main.o sum.o hello.o
$(CC) main.o sum.o hello.o -o hello

main.o: main.c
$(CC) $(CFLAGS) main.c

sum.o: sum.c
$(CC) $(CFLAGS) sum.c

hello.o: hello.c
$(CC) $(CFLAGS) hello.c

Method 5:

With this brief introduction to Makefiles, you can create some very sophisticated mechanism for compiling your projects.

CC=gcc
CFLAGS=-c -Wall
LDFLAGS=
SOURCES=main.c hello.c sum.c
OBJECTS=$(SOURCES:.cpp=.o)
EXECUTABLE=hello

all: $(SOURCES) $(EXECUTABLE)
$(EXECUTABLE): $(OBJECTS)
$(CC) $(LDFLAGS) $(OBJECTS) -o $@

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

If you understand this last example, you could adapt it to your own personal projects changing only 2 lines, no matter how many additional files you have !!!.

Thanks to:http://mrbook.org/tutorials/make/

The above examples is tested only on linux and Windows also supports make utility (through nmake utility), the readers are advised to work on their own in Windows. the following link will show you the way to nmake utility

http://msdn.microsoft.com/en-us/library/dd9y37ha(VS.71).aspx