[SDL] OT - Undefined references in my project

[Ulrich Eckhardt]

On Saturday 01 December 2007 13:24:44 Michael Sullivan wrote:
> CC=g++

No. CC is the C compiler, for C++ use CXX. Also, don't define those, 'make' 
knows defaults for them. Instead, if you need to override them, you can 
invoke make with

  CXX=g++-3.4 make

> CFLAGS=-W -Wall -pedantic

Dito, only that it's traditionally CXXFLAGS. Also, I'd rather not set them in 
the makefile. Neither of those make a difference though.

> LIBS=`sdl-config --cflags --libs` -lSDL_image -lSDL_gfx -lSDL_ttf

Okay, this one is definitely wrong: you want the output 
of 'sdl-config --cflags' in the CXXFLAGS, because if you put them into the 
LIBS var they simply don't work and also make no sense there. Note: what you 
need to set in the makefile is that part, therefore I'd do

  SDL_CFLAGS=`sdl-config --cflags`
  SDL_LIBS=`sdl-config --cflags` -lSDL_image -lSDL_gfx -lSDL_ttf

and then refer to those plus the user-overridable CFLAGS when compiling.

> character.o: character.cpp
> 	reset; $(CC) $(CFLAGS) -c character.cpp;rm *~

Just for your info: in order to get character.o, you neither need to 
invoke 'reset' (at least I think so) nor do you need to remove backup files 
(*~), so this only makes it harder for us to understand. Define separate 
targets for those. Further, you can use several lines for the target, also 
making it a bit easier to read. Lastly, if you change character.h, this will 
not(!) cause character.cpp to be recompiled like this! I'd suggest that you 
do a 

  HEADERS=battle.h character.h

and then define every target like

  battle.o: battle.cpp $(HEADERS)

Just to be on the safe side. Later, you can learn about determining the 
dependencies automatically to remove unnecessary ones. ;)

> battle.o: battle.cpp
> 	reset; $(CC) $(CFLAGS) -c battle.cpp -I/usr/include/SDL/; rm *~

You can remove the -I, if you put the output of 'sdl-config --cflags' into 
CFLAGS it will work without it. ;)

> all: battle.o character.o
> 	reset; $(CC) $(CFLAGS) battle.o character.o $(LIBS) -o battle; rm *~
>
> character.o and battle.o are created, but when I try to make all, I get
> the following errors:
>
> battle.o: In function `battle::battle()':
> battle.cpp:(.text+0x9e3): undefined reference to
> `Character::Character()'
[...]
> I don't understand why.  This is my first SDL project, and my first
> multifile C/C++ project, so I'm kinda out of my element here.

Maybe the above suggestions (in particular the missing header file dependency) 
already help. Otherwise, you should first try to compile a simple multi-file 
C++ project without SDL. Try to compile e.g. something like

  g++ -W -Wextra file1.cpp file2.cpp -o example

If that doesn't work, you did something wrong splitting the single file into 
multiple files. In any case, it has nothing to do with SDL then.

good luck

Uli