Makefile doesn't work

Question

I get this error when using my makefile:

make: Warning: File `makefile' has modification time 56 s in the future
make: Circular Menu.o <- Menu.o dependency dropped.
g++ a.out main.o Menu.o CourseList.o Course.o LecturerList.o StudentList.o Lecturer.o Student.o -o a.out
make: warning:  Clock skew detected.  Your build may be incomplete.

This is my makefile:

a.out: main.o Menu.o CourseList.o Course.o LecturerList.o StudentList.o Lecturer.o Student.o
g++ main.o Menu.o CourseList.o Course.o LecturerList.o StudentList.o Lecturer.o Student.o -o a.out

main.o: main.cpp Lecturer.o LecturerList.o Student.o StudentList.o Course.o CourseList.o Menu.o
g++ -c main.cpp

Menu.o: Menu.o Lecturer.o LecturerList.o Student.o StudentList.o Course.o CourseList.o
g++ -c Menu.cpp

CourseList.o: CourseList.cpp
g++ -c CourseList.cpp

Course.o: Course.cpp
g++ -c Course.cpp

LecturerList.o: LecturerList.cpp
g++ -c LecturerList.cpp

StudentList.o: StudentList.cpp
g++ -c StudentList.cpp

Lecturer.o: Lecturer.cpp
g++ -c Lecturer.cpp

Student.o: Student.cpp
g++ -c Student.cpp

Where's the error and how do I fix it? I'm aware to the fact it might be alittle confusing, but I hope someone here can help me with this problem, I'm breaking my head over this for hours... Thanks!!

NOTE: I edited the error and the makefile. Now I have only 1 problem

Answer 1

First, the problem with "File 'makefile' has modification time 56 s in the future" is a sysadmin problem. You are storing your files on a network file system. Your computer and the server computer don't agree on what time it is. To fix this, adjust the date on one or both of the computers so that they agree. To maintain that agreement, use something like "ntpd".

Second, the circular dependency is because you are confusing ".o" and ".cpp" files in your Makefile. Specifically, you are listing .o files as source dependencies for other .o files, which is (almost) never the case. Menu.o: Menu.o is one such circular dependency.

Third, the "file a.out not found" message is because you are specifying "a.out" as both an input and output file on your linker command line.

Here is one fixed version of your Makefile (don't forget to fix up the tabs if you copy-paste this into your editor.)

a.out: main.o Menu.o CourseList.o Course.o LecturerList.o StudentList.o Lecturer.o Student.o
  # Lose extraneous "a.out" on the next line.
  g++ main.o Menu.o CourseList.o Course.o LecturerList.o StudentList.o Lecturer.o Student.o -o a.out

# Get rid of all '.o' in the next line. They don't make any sense.
main.o: main.cpp 
  g++ -c main.cpp

# Change "Menu.o" to "Menu.cpp" and get rid of other .o files
Menu.o: Menu.cpp
  g++ -c Menu.cpp

CourseList.o: CourseList.cpp
  g++ -c CourseList.cpp

Course.o: Course.cpp
  g++ -c Course.cpp

LecturerList.o: LecturerList.cpp
  g++ -c LecturerList.cpp

StudentList.o: StudentList.cpp
  g++ -c StudentList.cpp

Lecturer.o: Lecturer.cpp
  g++ -c Lecturer.cpp

Student.o: Student.cpp
  g++ -c Student.cpp

Finally, your Makefile could be made much simpler and more readable if you were to use pattern rules and automatic variables.

Here is a much shorter version:

a.out: main.o Menu.o CourseList.o Course.o LecturerList.o StudentList.o Lecturer.o Student.o
  g++ $^ -o a.out

# Take advantage of Makefile's pattern match to avoid specifying every. single. file.
%.o: %.cpp 
  g++ -c $<

---

Reference: http://www.gnu.org/software/make/manual/make.html

Answer 2

The line

Menu.o: Menu.o Lecturer.o LecturerList.o Student.o StudentList.o Course.o CourseList.o

lists Menu.o as a requisite of Menu.o.

and a.out as listed is an input to g++ you should use -o to indicate that you want the output to go there.

Answer 3

I think you want

g++ -o a.out ...

not

g++ a.out ...

Also you can get rid of the circularity warning by not having Menu.o depend on Menu.o

Answer 4

The second line:

g++ a.out main.o Menu.o CourseList.o Course.o LecturerList.o StudentList.o Lecturer.o Student.o -o a.out

Is trying to compile a.out into a.out