title: Makefile warning: Warning: File `main.cpp' has modification time 2.1e+04 s in the future
body: <p>I have a working <code>Makefile</code>, but there is a warning that I couldn't fix. </p>
  
  <pre><code>#Use the g++ compiler
  CC = g++
  
  # Compiler flags:
  #   -Wall (most warnings enabled)
  #   -g (for debugging with gdb)
  CFLAGS = -Wall
  
  # Executable name:
  TARGET = deque_adt
  
  all: main.o deque_adt.o deque_adt
  
  $(TARGET): main.o deque_adt.o
      $(CC) $(CFLAGS) main.o deque_adt.o -o $(TARGET)
  
  main.o: main.cpp deque_adt.h 
      $(CC) $(CFLAGS) main.cpp -c
  
  deque_adt.o: deque_adt.cpp deque_adt.h
      $(CC)  $(CFLAGS) deque_adt.cpp -c
  
  clean:
      rm *.o *~ $(TARGET)
  </code></pre>
  
  <p>error:</p>
  
  <pre><code>make: Warning: File `main.cpp' has modification time 2.1e+04 s in the future
  g++ -Wall main.cpp -c
  g++  -Wall deque_adt.cpp -c
  g++ -Wall main.o deque_adt.o -o deque_adt
  make: warning:  Clock skew detected.  Your build may be incomplete.
  </code></pre>
  
  <p>Can someone help me out to figure out the problem? I have tried to switch between the elements but it still gives the same warning.</p>