Makefiles

file1.cpp

#include "file1.h"
#include <iostream>

void f1(){
    std::cout << "hello from file 1\n";
}

file1.h

#ifndef FILE1 
#define FILE1 
void f1();
#endif

file2.cpp

#include "file2.h"
#include <iostream>

void f2(){
    std::cout << "hello from file 2\n";
}

file2.h

#ifndef FILE2
#define FILE2
void f2();
#endif

file3.cpp

#include "file3.h"
#include <iostream>

void f3(){
    std::cout << "hello from file 3\n";
}

file3.h

#ifndef FILE3 
#define FILE3 
void f3();
#endif

main.cpp

#include "file1.h"
#include "file2.h"
#include "file3.h"
#include <cstdlib>
#include <iostream>

int main(){
    f1();
    f2();
    f3();
    return EXIT_SUCCESS;
}

Makefile

#targetname: prereqs
#	command

all:files

files:file1.o file2.o file3.o main.o
	g++ file1.o file2.o file3.o main.o -o files

file1.o:file1.cpp file1.h
	g++ -Wall -Werror -std=c++14 -c file1.cpp


file2.o:file2.cpp file2.h
	g++ -Wall -Werror -std=c++14 -c file2.cpp

file3.o:file3.cpp file3.h
	g++ -Wall -Werror -std=c++14 -c file3.cpp


main.o:main.cpp file1.h file2.h file3.h
	g++ -Wall -Werror -std=c++14 -c main.cpp

.PHONY:clean
clean:
	rm -f file1.o file2.o file3.o

Makefile-fancy

#targetname: prereqs
#	command
CC=g++
all:files
OBJECTS = file1.o file2.o file3.o main.o
CXXFLAGS = -Wall -Werror -std=c++14

files:$(OBJECTS)
	$(CC) $(OBJECTS) -o files
%.o:%.cpp *.h
	  $(CC) $(CXXFLAGS) -c $<

.PHONY:clean
clean:
	rm -f $(OBJECTS) files

voidpointers.cpp

#include <iostream>
#include <cstdlib>

typedef void * operation (void*, void *);


void * intadd(void * a, void * b)
{
    *(int*)a += *(int*)b;
    return a;
}

void * intsub(void * a, void * b){
    *(int*)a -= *(int*)b;
    return a;
}

void * dbladd(void * a, void * b){
    *(double*)a += *(double*)b;
    return a;
}

void * dblsub(void * a, void * b) {
    *(double*)a -= *(double *)b;
    return a;
}


void * perform(void* a, void* b, operation op) {
    return op(a,b);
}

int main(void){
    int a,b;
    a=3;
    b=4;
    std::cout << "3 + 4 is:";
    perform(&a,&b,intadd);
    std::cout << a << std::endl;

    a=3;
    b=4;
    std::cout << "3 - 4 is:";
    perform(&a,&b,intsub);
    std::cout << a << std::endl;

    double da, db;
    da=3.3;
    db=4.4;

    std::cout << "3.3+4.4 is ";
    perform(&da,&db,dbladd);
    std::cout << da << std::endl; 

    da=3.3;
    db=4.4;

    std::cout << "3.3-4.4 is ";
    perform(&da,&db,dblsub);
    std::cout << da << std::endl;
  
    return EXIT_SUCCESS;
}