Make File and SDL with multiple files - console

Question

My project is to make a simple little screen with some moving sprite using SDL in Linux, but I don't want to use an IDE. My goal is get a better understanding of makefiles and all that business; however, I've run into a wall that I can't seem to get past. I'm hoping that someone can explain why what I have is wrong and what I can do to avoid it!
So, my program has multiple dependencies that sort of cascade through each of the files--as such I have all the dependencies listed as need be in the makefile. Here is my code...
OUT=program
CC=g++
SDL=-lSDLmain -lSDL -lSDL_image -lSDL_ttf
all: constants globals functions sprite sprite_test
${CC} sprite_driver.o sprite.o functions.o globals.o constants.h -o ${OUT} ${SDL}
constants:
${CC} -c constants.h
globals: constants
${CC} -c globals.cpp globals.h constants.h ${SDL}
functions: constants globals
${CC} -c functions.cpp globals.h globals.o constants.h ${SDL}
sprite: constants globals functions
${CC} -c sprite.cpp functions.o globals.o constants.h ${SDL}
sprite_test: constants globals functions sprite
${CC} -c sprite_driver.cpp sprite.o functions.o globals.o constants.h ${SDL}
By the time the compiler reaches the functions, it says that the globals.o has not been properly linked. Inside this file are many external declarations that aren't recognized later in the compilation so it looks like there are multiple declarations of the same variables. Here's what the console spits out.
g++ -c constants.h
g++ -c globals.cpp globals.h constants.h -lSDLmain -lSDL -lSDL_image -lSDL_ttf
g++ -c functions.cpp globals.h globals.o constants.h -lSDLmain -lSDL -lSDL_image -lSDL_ttf
g++: warning: globals.o: linker input file unused because linking not done
g++ -c sprite.cpp functions.o globals.o constants.h -lSDLmain -lSDL -lSDL_image -lSDL_ttf
g++: warning: functions.o: linker input file unused because linking not done
g++: warning: globals.o: linker input file unused because linking not done
g++ -c sprite_driver.cpp sprite.o functions.o globals.o constants.h -lSDLmain -lSDL -lSDL_image -lSDL_ttf
g++: warning: sprite.o: linker input file unused because linking not done
g++: warning: functions.o: linker input file unused because linking not done
g++: warning: globals.o: linker input file unused because linking not done
g++ sprite_driver.o sprite.o functions.o globals.o constants.h -o program -lSDLmain -lSDL -lSDL_image -lSDL_ttf
sprite.o:(.bss+0x0): multiple definition of `screen'
sprite_driver.o:(.bss+0x0): first defined here
sprite.o:(.bss+0x4): multiple definition of `event'
sprite_driver.o:(.bss+0x4): first defined here
sprite.o:(.bss+0x18): multiple definition of `keystate'
sprite_driver.o:(.bss+0x18): first defined here
sprite.o:(.bss+0x1c): multiple definition of `font'
sprite_driver.o:(.bss+0x1c): first defined here
sprite.o:(.bss+0x20): multiple definition of `t_black'
sprite_driver.o:(.bss+0x20): first defined here
functions.o:(.bss+0x0): multiple definition of `screen'
sprite_driver.o:(.bss+0x0): first defined here
functions.o:(.bss+0x4): multiple definition of `event'
sprite_driver.o:(.bss+0x4): first defined here
functions.o:(.bss+0x18): multiple definition of `keystate'
sprite_driver.o:(.bss+0x18): first defined here
functions.o:(.bss+0x1c): multiple definition of `font'
sprite_driver.o:(.bss+0x1c): first defined here
functions.o:(.bss+0x20): multiple definition of `t_black'
sprite_driver.o:(.bss+0x20): first defined here
collect2: error: ld returned 1 exit status
make: *** [all] Error 1

Answer 1

You've got so much wrong here that I think you might need to get some introductory materials and go through them. SO is not really the right place to learn these tools from scratch: there are lots of resources for that.
A few things:
You do not compile .h (header) files.
You do not list header files on the compile or link command line when you compile .c (source) files.
You do not list .o (object) files on the compile command line when you compile a source file into an object file. You only put object files on the link command line.
You do not list -l... (library) files on the compile command line when you compile a source file into an object file. You only put library files on the link command line.
Your makefile rules must use the actual file you're trying to create as the target, not just a word you choose.
By long-standing convention, the CC variable in makefiles stands for the C compiler. You're trying to compile C++ source, so you should use the CXX variable.
The make program has a lot of built-in rules on how to build various kinds of files, and one of them describes how to build an object file from a .cpp (C++ source) file. Taking advantage of that you can write your makefile very simply as:
OUT = program
CXX = g++
SDL = -lSDLmain -lSDL -lSDL_image -lSDL_ttf
OBJECTS = sprite_driver.o sprite.o functions.o globals.o
all: $(OUT)
$(OUT): $(OBJECTS)
$(CXX) -o $# $^ ${SDL}
$(OBJECTS): constants.h