Automate the compilation process for a multiple file C project

Suppose a C program consists of 2 C program files:

f1.c 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 );                       
}  
#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 );   
}

In addition, we have the header file f2.h for f2.c: 

// header file f2.h

void print ( double x ) ;
double square( double x ) ;

Automate the compilation process for a multiple file C project

  • Suppose the executable program is: 

       main

  • The chain of file dependencies, starting from the target main: 

      main  depends on:            f1.o f2.o
        constructed using:     gcc -o main  f1.o f2.o
            
  f1.o  depends on:            f1.c
        constructed using:     gcc -c f1.c

  f2.o  depends on:            f2.c 
        constructed using:     gcc -c f2.c

  • However, there are more dependencies...  

    Hint:   look for #include files !

Automate the compilation process for a multiple file C project

Notice that the files f1.c and f2.c #includes the header file f2.h:

f1.c 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 );                       
}  
#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 );   
}

When the header file f2.h is updated, the change is included inside f1.c and f2.c

Automate the compilation process for a multiple file C project

  • The complete chain of file dependencies includes the header files: 

      main  depends on:            f1.o f2.o
        constructed using:     gcc -o main  f1.o f2.o
            
  f1.o  depends on:            f1.c 
        constructed using:     gcc -c f1.c

  f2.o  depends on:            f2.c 
        constructed using:     gcc -c f2.c 

  f1.c  depends on:            f2.h
        constructed using:     ???

  f2.c  depends on:            f2.h
        constructed using:     ???

  • However:

    • There are no commands needed to created the result file...

Automate the compilation process for a multiple file C project

  • We can simplify the chain of file dependencies as follows: 

      main  depends on:            f1.o f2.o
        constructed using:     gcc -o main  f1.o f2.o
            
  f1.o  depends on:            f1.c f2.h
        constructed using:     gcc -c f1.c

  f2.o  depends on:            f2.c f2.h
        constructed using:     gcc -c f2.c

  • Effect:

    • When the header file f2.h is updated, we will execute: 

         gcc -c f1.c
   gcc -c f2.c

      (That's what we really want to do !)

Automate the compilation process for a multiple file C project

  • Writing a Makefile for this chain of file dependencies: 

      main  depends on:            f1.o f2.o
        constructed using:     gcc -o main  f1.o f2.o
            
  f1.o  depends on:            f1.c f2.h
        constructed using:     gcc -c f1.c

  f2.o  depends on:            f2.c f2.h
        constructed using:     gcc -c f2.c

  • Makefile: 

    
main: f1.o f2.o
        gcc -o main f1.o f2.o

f1.o:  f1.c  f2.h
        gcc -c f1.c

f2.o:  f2.c  f2.h

Automate the compilation process for a multiple file C project

  • Writing a Makefile for this chain of file dependencies: 

      main  depends on:            f1.o f2.o              
        constructed using:     gcc -o main  f1.o f2.o 
            
  f1.o  depends on:            f1.c f2.h
        constructed using:     gcc -c f1.c

  f2.o  depends on:            f2.c f2.h
        constructed using:     gcc -c f2.c

  • Makefile: 

    main: f1.o f2.o
        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

Automate the compilation process for a multiple file C project

  • Writing a Makefile for this chain of file dependencies: 

      main  depends on:            f1.o f2.o
        constructed using:     gcc -o main  f1.o f2.o
            
  f1.o  depends on:            f1.c f2.h   
        constructed using:     gcc -c f1.c 

  f2.o  depends on:            f2.c f2.h
        constructed using:     gcc -c f2.c

  • Makefile: 

    main: f1.o f2.o
        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

Automate the compilation process for a multiple file C project

  • Writing a Makefile for this chain of file dependencies: 

      main  depends on:            f1.o f2.o
        constructed using:     gcc -o main  f1.o f2.o
            
  f1.o  depends on:            f1.c f2.h
        constructed using:     gcc -c f1.c

  f2.o  depends on:            f2.c f2.h   
        constructed using:     gcc -c f2.c

  • Makefile: 

    main: f1.o f2.o
        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

DEMO: demo/C/Make/2