我如何使我的makefile创建第二个可执行文件？

Question

all:  exe1 exe2

exe1: obj1
     g++ -Wall -Werror -std=c++11 program1.o -o program1  -lgtest

obj1:
     g++ -c -Wall -Werror -std=c++11 program1.cc

exe2: obj2
     g++ -Wall -Werror -std=c++11 program2.o -o program2

obj2:
     g++ -c -Wall -Werror -std=c++11 program2.cc

clean:
     rm *.o *.exe

当我运行生成文件时，仅目标exe1被编译并创建为可执行文件。如果我仅将目标设为exe2，则会收到错误消息

make: Nothing to be done for `all'.

如何使exe2对Makefile可见？

Answer 1

makefile可能看起来应该更像这样：

# Set the dependencies to the names of the executables you
# want to build
all:  program1 program2

#
# Make uses some variables to define tools.
# The most important for you is CXX: Which is set to the C++ compiler.

#
# Notice that target name should match the executable name.
#     This is because `make` will check its existence and creation date
#     against its dependenc(ies) existence and creation date.
program1: program1.o
     $(CXX) -Wall -Werror -std=c++11 program1.o -o program1  -lgtest

program2: program2.o
     $(CXX) -Wall -Werror -std=c++11 program2.o -o program2

#
# We can generalize the creation of the object file.
%.o: %.cc
     $(CXX) -c -Wall -Werror -std=c++11 $*.cc

clean:
     $(RM) *.o *.exe

Answer 2

“ make”实用程序有许多规则可以简化标准构建。 Makefile的压缩版可以是：

PROGRAMS = program1 program2

all: $(PROGRAMS)

CXXFLAGS=-Wall -Werror -std=c++11 

# Link program1 with the gtest library
program1: LDLIBS=-lgtest

clean:
     $(RM) $(PROGRAMS) *.o

# Following section is needed only for binaries that need more than one object.
# Does not apply in the this case, since program1 depends only on program1.o.
# Included for allow extending the makefile.

program3: program3.o second.o # Additional objects here.