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Example of make file for a multi-file C program project

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• Creating a Makefile for a multi-files C program
  • Now consider a C program that consists of 2 program files:

    We have a C programming project that consists of 2 program files: f1.c    contains the main( ) function        f2.c    contains library functions The header file for the library functions in f2.c is: f2.h     The executable program name that we want to create is called: main     This is the final target

    The content of the various files are as follows:

    f1.c	f2.h	f2.c
    #include <stdio.h> #include "f2.h" int main( int argc, char *argv[] ) { double a, b; a = 4.0; b = square( a ); print( a ); print( b ); }	void print ( double x ) ; double square( double x ) ;	#include <stdio.h> #include "f2.h" void print ( double x ) { printf("Number = %lf\n", x ); } double square( double x ) { double r; r = x * x; return ( r ); }

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  • To compile this project, you will use the following commands (see: click here )

    gcc -c f1.c (f1.c ---> f1.o) gcc -c f2.c (f2.c ---> f2.o) gcc -o main f1.o f2.o (f1.o, f2.o ---> main)

    We can easily discern the following file dependencies:

    1. f1.o: f1.c 2. f2.o: f2.c 3. main: f1.o f2.o

    However:

    Notice that the program file p1.c and p2.c both included the header file h2.h !!! That means: If the header file f2.h is updated, then it will affect the outcome of the compilation of the program file p1.c and p2.c !!!

    Therefore, the actualy file dependencies are:

    1. f1.o: f1.c f2.h 2. f2.o: f2.c f2.h 3. main: f1.o f2.o

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  • We can now create (edit) the follow Makefile that represents the above file dependencies and their maintenance comamnds:

    main: f1.o f2.o # We usually put the final target first gcc -o main f1.o f2.o f1.o: f1.c f2.h gcc -c f1.c f2.o: f2.c f2.h gcc -c f2.c

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  • Example Program: (Demo above code)                                                
    • Prog file: /home/cs255001/demo/C/Make/2/*

    How to run the program:

    To compile:   make TARGET          Observe which commands are run by the make utility

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  • Result:

    The first time we run make, you will see: UNIX>> make gcc -c f1.c gcc -c f2.c gcc -o main f1.o f2.o and the make utility creates the target main Now, run make again, and you will see: UNIX>> make `main' is up to date. The make utility has determined that main is more recent than the dependency file func5a.o and func5b.o and skips the compilation process !!! Next, edit f1.c (add a space somewhere in the program), save it and then run make again: UNIX>> make gcc -c f1.c gcc -o main f1.o f2.o The make utility has determined that f1.o is out-of-date and runs: gcc -c f1.c and creates a up-to-date f1.o However, the new f1.o will make main out-of-date !!! So make executes: gcc -o main f1.o f2.o and creates a new main program !!! Finally, edit header file func5b.h (add a space somewhere in the program), save it and then run make again: UNIX>> make gcc -c f1.c gcc -c f2.c gcc -o main f1.o f2.o The make utility re-compiles both f1.c and f2.c because of the f1.o and f2.o depends on f2.h: f1.o: f1.c f2.h gcc -c f1.c f2.o: f2.c f2.h gcc -c f1.c