C ++在编译时未定义对“ main”的引用

Question

After try to use this attached makefile the error that appears is :

(.text+0x20): undefined reference to `main'

collect2: error: ld returned 1 exit status

make: *** [Ass1F] Error 1

the makefile is :

all: Ass1F

Ass1F: bin/main.o bin/x.o bin/y.o bin/z.o bin/w.o
g++ -o bin/main.o bin/x.o bin/y.o bin/z.o bin/w.o

@echo 'Finished building target: Ass1F'
@echo ' '

bin/x.o: src/x.cpp
g++ -g -Wall -Weffc++ -c -Linclude -o bin/x.o src/x.cpp

bin/y.o: src/y.cpp
g++ -g -Wall -Weffc++ -c -Linclude -o bin/y.o src/y.cpp

bin/z.o: src/z.cpp
g++ -g -Wall -Weffc++ -c -Linclude -o bin/z.o src/z.cpp

bin/w.o: src/w.cpp
g++ -g -Wall -Weffc++ -c -Linclude -o bin/w.o   src/w.cpp

bin/main.o: src/main.cpp
g++ -g -Wall -Weffc++ -c -Linclude -o bin/main.o src/main.cpp

clean: 
rm -f bin/*

what should I do with this problem? the reason is the makefile or something in the code? just to let you know we used eclipse to write the code and everything work perfectly- no any bugs.

thanks

Answer 1

Line g++ -o bin/main.o bin/xo bin/yo bin/zo bin/wo tries to create executable named bin/main.o , overwriting its previous contents.

It should be eg g++ -o Ass1F bin/main.o bin/xo bin/yo bin/zo bin/wo

Answer 2

Your makefile recipe for Ass1F is incorrect, it doesn't specify the output file, os make uses bin/main.o as the output file instead of one of the input files.

You can simplify the makefile by using pattern rules (ie with wildcards) and using pre-defined variables such as $@ (the name of the target) and $^ (the list of prerequisites) and CXX (the C++ compiler):

CXXFLAGS  = -g -Wall -Weffc++
CPPFLAGS =
LDFLAGS =
LDLIBS =

all: Ass1F

Ass1F: bin/main.o bin/x.o bin/y.o bin/z.o bin/w.o
        $(CXX) $(LDFLAGS) -o $@ $^ $(LDLIBS)
        @echo 'Finished building target: Ass1F'
        @echo ' '

bin/%.o: src/%.cpp
        $(CXX) $(CPPFLAGS) $(CXXFLAGS) -c -o $@ $^

clean: 
        rm -f bin/*