Linux makefile 中未定义的引用
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Undefined references in makefile
提问by Bartlomiej Lewandowski
Ok, ive read about 10 tutorials, but i keep getting errors all the time, i have 5 files, main.cpp class.cpp, class.h and functions.cpp and functions.h. All of those use functions from different objects meaning that functions in functions.cpp uses objects from classes.cpp.
好吧，我读了大约 10 个教程，但我一直都在出错，我有 5 个文件，main.cpp class.cpp、class.h 和 functions.cpp 和 functions.h。所有这些都使用来自不同对象的函数，这意味着functions.cpp 中的函数使用来自classes.cpp 的对象。
My makefile looks as follows
我的 makefile 如下所示
CC = g++ -O2 -I./sdl/include -L.
LIBS = -lm -lSDL -lpthread -ldl
SRC = main.cpp
SDLF = SDLfunctions.cpp
CLASS = classes.cpp
CLASSH = classes.h
SDLFH = SDLfunctions.h
all: main
main: SDLfunctions.o Classes.o $(SRC)
$(CC) -o $@ $(SRC) $(LIBS)
SDLfunctions.o: $(SDLFH) $(SDLF) $(CLASS) $(CLASSH)
$(CC) -o $@ $(SDLF) $(LIBS)
Classes.o: $(CLASS) $(CLASSH) $(SDLF) $(SDLFH)
$(CC) -o $@ $(CLASS) $(LIBS)
I keeps telling me that it has undefined references. What am i missing?
我一直告诉我它有未定义的引用。我错过了什么？
What makefile outputs
什么makefile输出
/usr/lib/i386-linux-gnu/gcc/i686-linux-gnu/4.5.2/../../../crt1.o: In function `_start':
(.text+0x18): undefined reference to `main'
/tmp/ccJG6yQA.o: In function `DrawEnemies(SDL_Surface*)':
SDLfunctions.cpp:(.text+0x3a7): undefined reference to `Enemy::sprite'
/tmp/ccJG6yQA.o: In function `rysujpociski(int, SDL_Surface*, SDL_Surface*,
std::vector<AllyBullet, std::allocator<AllyBullet> >&, double)':
SDLfunctions.cpp:(.text+0x141f): undefined reference to `AllyBullet::sprite'
/tmp/ccJG6yQA.o: In function `global constructors keyed to width':
SDLfunctions.cpp:(.text+0x14a7): undefined reference to `Enemy::Enemy()'
collect2: ld returned 1 exit status
make: *** [SDLfunctions.o] Error 1
The files compile great when i had them in Visual C++, so it has to be my makefile.
当我在 Visual C++ 中使用它们时，这些文件编译得很好，所以它必须是我的 makefile。
采纳答案by Shahbaz
You are indeed doing something strange. What you should is to compile (-c) the object files and then link them together. This would look like this:
你确实在做一些奇怪的事情。您应该编译 ( -c) 目标文件，然后将它们链接在一起。这看起来像这样：
CC = g++ -O2 -I./sdl/include -L.
LIBS = -lm -lSDL -lpthread -ldl
SRC = main.cpp
SDLF = SDLfunctions.cpp
CLASS = classes.cpp
CLASSH = classes.h
SDLFH = SDLfunctions.h
all: main
main: SDLfunctions.o Classes.o $(SRC)
$(CC) -o $@ $(SRC) SDLfunctions.o Classes.o $(LIBS) # you forgot to link
# the object files
SDLfunctions.o: $(SDLFH) $(SDLF) $(CLASS) $(CLASSH)
$(CC) -o $@ -c $(SDLF) # -c added to compile, not link
Classes.o: $(CLASS) $(CLASSH) $(SDLF) $(SDLFH)
$(CC) -o $@ -c $(CLASS) # -c added to compile, not link
While you are doing this, it is even better if you compiler main.o separately also. Therefore:
当你这样做时，如果你也单独编译 main.o 会更好。所以：
CC = g++ -O2 -I./sdl/include -L.
LIBS = -lm -lSDL -lpthread -ldl
MAIN = main.cpp
SDLF = SDLfunctions.cpp
CLASS = classes.cpp
CLASSH = classes.h
SDLFH = SDLfunctions.h
all: main
main: SDLfunctions.o Classes.o main.o
$(CC) -o $@ SDLfunctions.o Classes.o main.o $(LIBS)
main.o: $(SDLFH) $(MAIN) $(CLASSH)
$(CC) -o $@ -c $(MAIN)
SDLfunctions.o: $(SDLFH) $(SDLF) $(CLASS) $(CLASSH)
$(CC) -o $@ -c $(SDLF)
Classes.o: $(CLASS) $(CLASSH) $(SDLF) $(SDLFH)
$(CC) -o $@ -c $(CLASS)
Also note that I removed the $(LIBS)when using -cbecause linking doesn't happen then.
另请注意，我$(LIBS)在使用时删除了，-c因为那时不会发生链接。
回答by Schwern
You have a typo. You're using $(CLASSESH)but declared CLASSH.
你有一个错字。您正在使用$(CLASSESH)但已声明CLASSH.
回答by Adrian Cornish
You are trying to link your .o files into executables. Add a -c to the compile flags so it compiles only for you object files.
您正在尝试将 .o 文件链接到可执行文件中。将 -c 添加到编译标志，以便它只为您的目标文件编译。
Make it the first option like this
使它成为这样的第一个选项
SDLfunctions.o: $(SDLFH) $(SDLF) $(CLASS) $(CLASSH)
$(CC) -c -o $@ $(SDLF) $(LIBS)
