C++ Makefile 错误 - 没有创建目标 '%.cpp' 的规则

Question

美好的一天，我正在学习编写自己的 makefile 的教程，我在这里找到了教程:

http://www.cs.colby.edu/maxwell/courses/tutorials/maketutor/

我知道本教程适用于 C 生成文件，但我相信 C 和 C++ 之间的相似性意味着生成文件的功能几乎没有区别(例如，我使用的是 g++ 而不是 gcc)。我希望我在这一点上的假设不是一个因素，因为之前的 4 个教程似乎都运行良好。

在教程中运行 Makefile 5 时，我收到有关从 .cpp 文件构建目标文件的错误:

制作:*** 没有制作目标“%.cpp”的规则，“obj”需要。停止。

我似乎无法弄清楚为什么会这样，非常困惑和沮丧，因为我觉得这不应该发生。我在下面包含了我的完整 Makefile，将不胜感激任何帮助:

 # Example Makefile                                                                                                                                                                                             
 # ----------------
 # Please remember to turn off the vim option: 'expandtab' so that tabs are 
 # actually displayed as tabs (do so like this - :set noexpandtab )
 #

 # This file specifies dependencies, which means that the two c++ files must
 # be compiled before the executable is built

 # ------------------
 # Makefile Constants
 # ------------------

 # Directory constants
 IDIR =../include  # Specifies location of include directory
 ODIR =obj        # Specifies location of object directory
 LDIR =../lib      # Specifies location of library directory

 LIBS=-lm  # ?

 # Options constants
 CC=g++            # Specifies the specific C compiler to use, g++ specifies C++ compiler
 CFLAGS=-I$(IDIR)  # List of flags to pass to compilation command

 # Dependency Constants
 DEP_FILES=helloMake.h                      # Specifies dependency files
 DEPS=$(patsubst %,$(IDIR)/%,$(DEP_FILES))  # Specifies path to dependencies and dependency files

 # Object constants
 OBJ_FILES=helloMake.o helloFunc.o         # Specify object files
 OBJ=$(patsubst %,$(ODIR)/%,$(OBJ_FILES))  # Specifies path to objects and object files


 # -----------
 # Compilation
 # -----------

 # Specify rules to make object files
 $(ODIR)/%.o: %.cpp $(DEPS)       # Specifies that .o files depend on the .cpp version of the file and the .h files included in the DEPS macro
     $(CC) -c -o $@ $< $(CFLAGS)  # The -c flag says to generate the object file, the -o $@ says to put the output of the compilation in the
                                  # file named on the left side of the : the $< is the first item in the dependencies list

 # Specify rules to make target executable
 helloMake: $(OBJ)                     # Target : Dependencies
     $(CC) -o $@ $^ $(CFLAGS) $(LIBS)  # This is the actual compilation command

 .PHONY: clean  # Prevent the make command from attempting to do something with a file named 'clean'

 # Specify rules to clean the object files
 clean:
     rm -f $(ODIR)/*.o *~ core $(INCDIR)/*~  # Removes all compiled object files

Answer 1

不幸的是，这个“简单”的教程助长了不良做法。

基本上，您首先需要一个正确的 C Makefile:

# Specify the final target name
EXE := helloMake

# Specify the source files
# Effectively list all source files in the current directory
SRC := $(wildcard *.c)

# From the source file list, get the corresponding object file list
# This is a clearer syntax for $(patsubst %.c,%.o,$(SRC))
OBJ := $(SRC:.c=.o)

# From the object file list, get the dependency file list to handle automatic
# recompilation when a header file is modified
DEP := $(OBJ:.o=.d)

# Specify preprocessor flags (this is a built-in variable)
CPPFLAGS := -I../include
# Required flags to enable the automatic dependency generation by the compiler
CPPFLAGS += -MMD -MP

# Specify compiler flags (this is a built-in variable)
# Here some basic warning flags
CFLAGS := -Wall -W -pedantic

# Specify linker flags (this is a built-in variable)
LDFLAGS := -L../lib

# Specify linker libraries (this is a built-in variable)
# m is the maths library
LDLIBS := -lm

# Tell make that these target are not real files
.PHONY: all clean

# Now the standard primary rule
all: $(EXE)

# How do we make $(EXE) ? Remember the recipe describe the linking phase
$(EXE): $(OBJ)
    $(CC) $(LDFLAGS) $^ $(LDLIBS) -o $@

# Let's clean up the mess
clean:
    $(RM) $(EXE) $(OBJ) $(DEP)

# Don't forget to include the dependency files to let make know when to recompile
-include $(DEP)

然后你需要知道 C Makefile 和 C++ Makefile 之间的区别:

• 使用$(CXX)代替$(CC),
• 使用$(CXXFLAGS)代替$(CFLAGS),
• 使用 .cpp 代替 .c。

大功告成。

# Specify the final target name
EXE := helloMake

# Specify the source files
# Effectively list all source files in the current directory
SRC := $(wildcard *.cpp)

# From the source file list, get the corresponding object file list
# This is a clearer syntax for $(patsubst %.cpp,%.o,$(SRC))
OBJ := $(SRC:.cpp=.o)

# From the object file list, get the dependency file list to handle automatic
# recompilation when a header file is modified
DEP := $(OBJ:.o=.d)

# Specify preprocessor flags (this is a built-in variable)
CPPFLAGS := -I../include
# Required flags to enable the automatic dependency generation by the compiler
CPPFLAGS += -MMD -MP

# Specify compiler flags (this is a built-in variable)
# Here some basic warning flags
CXXFLAGS := -Wall -W -pedantic

# Specify linker flags (this is a built-in variable)
LDFLAGS := -L../lib

# Specify linker libraries (this is a built-in variable)
# m is the maths library
LDLIBS := -lm

# Tell make that these target are not real files
.PHONY: all clean

# Now the standard primary rule
all: $(EXE)

# How do we make $(EXE) ? Remember the recipe describe the linking phase
$(EXE): $(OBJ)
    $(CXX) $(LDFLAGS) $^ $(LDLIBS) -o $@

# Let's clean up the mess
clean:
    $(RM) $(EXE) $(OBJ) $(DEP)

# Don't forget to include the dependency files to let make know when to recompile
-include $(DEP)

---

编辑:为了能够重新定位构建文件(.o 和 .d 文件)，您需要进行一些调整:

# Specify the final target name
EXE := helloMake

# Specify the source files
# Effectively list all source files in the current directory
SRC := $(wildcard *.cpp)

# Specify where to put the build temporary files
BLD := obj

# From the source file list, get the corresponding object file list
# This is a clearer syntax for $(patsubst %.cpp,$(BLD)/%.o,$(SRC))
OBJ := $(SRC:%.cpp=$(BLD)/%.o)

# From the object file list, get the dependency file list to handle automatic
# recompilation when a header file is modified
DEP := $(OBJ:.o=.d)

# Specify preprocessor flags (this is a built-in variable)
CPPFLAGS := -I../include
# Required flags to enable the automatic dependency generation by the compiler
CPPFLAGS += -MMD -MP

# Specify compiler flags (this is a built-in variable)
# Here some basic warning flags
CXXFLAGS := -Wall -W -pedantic

# Specify linker flags (this is a built-in variable)
LDFLAGS := -L../lib

# Specify linker libraries (this is a built-in variable)
# m is the maths library
LDLIBS := -lm

# Tell make that these target are not real files
.PHONY: all clean

# Now the standard primary rule
all: $(EXE)

# How do we make $(EXE) ? Remember the recipe describe the linking phase
$(EXE): $(OBJ)
    $(CXX) $(LDFLAGS) $^ $(LDLIBS) -o $@

# The build directory is custom so we need to tell make how to do it
# The build directory must exist before trying to compile
$(BLD)/%.o: %.cpp | $(BLD)
    $(CXX) $(CPPFLAGS) $(CXXFLAGS) -o $@ -c $<

# Simple rule to create the build directory if needed
$(BLD):
    mkdir $@

# Let's clean up the mess, we can just remove the build directory alonside the executable
clean:
    $(RM) -r $(BLD) $(EXE)

# Don't forget to include the dependency files to let make know when to recompile
-include $(DEP)