How to compile with a makefile without deleting .o files?

Question

I've no experience at all with makefiles, but I managed to get mine working. However, when I modify a file and want the new version to get compiled again, I've just noticed that I need to delete de .o file generated previously to make the new compilation (otherwhise, I am told that nothing can be done).

Is there any option that can be added to a makefile to make it replace an old .o (only if it is an older version) with the new one? Or, at least, that's what I think my solution could be.

Thanks in advance,

Eduardo

PD: Here you have my Makefile, in case you need it.

todo: Sensor Control Lista

#Ficheros de los que depende
Sensor: Sensor.o semaforo.o memocomp.o colamsg.o
    #Cómo crea esos ficheros
    g++ Sensor.o semaforo.o memocomp.o colamsg.o -o Sensor -lrt -lpthread

Control: Control.o semaforo.o memocomp.o colamsg.o
    g++ Control.o semaforo.o memocomp.o colamsg.o -o Control -lrt -lpthread

Lista: Lista.o semaforo.o memocomp.o colamsg.o
    g++ Lista.o semaforo.o memocomp.o colamsg.o -o Lista -lrt -lpthread

#Compilación de cada uno de esos ficheros
Sensor.o: Sensor.cpp semaforo.hpp memocomp.hpp colamsg.hpp
    g++ -c Sensor.cpp

Control.o: Control.cpp semaforo.hpp memocomp.hpp colamsg.hpp
    g++ -c Control.cpp

Lista.o: Lista.cpp semaforo.hpp memocomp.hpp colamsg.hpp
    g++ -c Lista.cpp

semaforo.o: semaforo.cpp semaforo.hpp
    g++ -c semaforo.cpp

memocomp.o: memocomp.cpp memocomp.hpp
    g++ -c memocomp.cpp

colamsg.o: colamsg.cpp colamsg.hpp
    g++ -c colamsg.cpp


#Elimina los ficheros creados previamente por el usuario ****
clean:
    rm /dev/shm/sem.1207*
    rm /dev/shm/1207*
    rm /dev/mqueue/1207*

Read more about `make`; try `make -p` to understand the builtin rules. Look at [this](http://stackoverflow.com/a/14180540/841108) — Basile Starynkevitch, Dec 07 '15 at 15:49

score 1 · Accepted Answer · answered Dec 07 '15 at 15:44

1

Usage: make [options] [target] ...
Options:
  -b, -m                      Ignored for compatibility.
  -B, --always-make           Unconditionally make all targets.
...etc

answered Dec 07 '15 at 15:44

Richard Hodges

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score 0 · Answer 2 · answered Dec 07 '15 at 15:43

0

colamsg.o: colamsg.cpp colamsg.hpp
^target    ^dependencies

As long as all the dependencies are listed for each target, you don't have to do anything.

Make will notice that the object file is out of date.

answered Dec 07 '15 at 15:43

Karoly Horvath

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I haven't managed to make it work that way, but it's surely my fault! – eduherminio Dec 07 '15 at 16:07
But this is exactly what you've done!!! This is the better answer than the one you selected. – Jean-Baptiste Yunès Dec 07 '15 at 16:09
Check the dates of the files, maybe the `.o`-s were generated in a system with wrong clock, or your FS doesn't update modification times... – Karoly Horvath Dec 07 '15 at 16:09
Using WIndows doesn't work, but using Linux does (with no need to add dependencies). – eduherminio Dec 07 '15 at 19:01

How to compile with a makefile without deleting .o files?

2 Answers2