I'm currently writing small simple C programs. As of now my Makefiles have consisted of text something along the lines of:
program_name:
clang -o program_name program_name.c
Is this all I need? I wasn't sure if I needed to establish dependencies between .o and .h files, even if they don't necessarily exist in my project.
You are working too hard. You should simplify your Makefile to 2 lines:
CC=clang
program_name: some.h
There is no need to specify the dependency on program_name.o or program_name.c, since those are implied. There is also no need to give the rule explicitly, since you are using the default rule. Dependencies on header files do need to be spelled out, however.
I use GNU Make myself. Not sure what you're using. For GNU Make, refer to:
http://www.gnu.org/prep/standards/html_node/Makefile-Conventions.html#Makefile-Conventions
http://www.gnu.org/software/make/
Is this all I need?
No.
I wasn't sure if I needed to establish dependencies between .o and .h files
Generally, you should, especially if you're using custom data types (and even if not: a change in a function signature can break the whole program if the ABI/calling conventions on your platform consist of black magic).
The template I'm using is usually:
CC = gcc
LD = $(CC)
CFLAGS = -c -Wall
LDFLAGS = -lwhatever -lfoo -lbar
TARGET = myprog
OBJECTS = $(patsubst %.c, %.o, $(wildcard *.c))
all: $(TARGET)
$(TARGET): $(OBJECTS)
$(LD) $(LDFLAGS) -o $# $^
%.c: %.h
%.o: %.c
$(CC) $(CFLAGS) -o $# $^
Related
I have the following makefile that I use to build a program (a kernel, actually) that I'm working on. Its from scratch and I'm learning about the process, so its not perfect, but I think its powerful enough at this point for my level of experience writing makefiles.
AS = nasm
CC = gcc
LD = ld
TARGET = core
BUILD = build
SOURCES = source
INCLUDE = include
ASM = assembly
VPATH = $(SOURCES)
CFLAGS = -Wall -O -fstrength-reduce -fomit-frame-pointer -finline-functions \
-nostdinc -fno-builtin -I $(INCLUDE)
ASFLAGS = -f elf
#CFILES = core.c consoleio.c system.c
CFILES = $(foreach dir,$(SOURCES),$(notdir $(wildcard $(dir)/*.c)))
SFILES = assembly/start.asm
SOBJS = $(SFILES:.asm=.o)
COBJS = $(CFILES:.c=.o)
OBJS = $(SOBJS) $(COBJS)
build : $(TARGET).img
$(TARGET).img : $(TARGET).elf
c:/python26/python.exe concat.py stage1 stage2 pad.bin core.elf floppy.img
$(TARGET).elf : $(OBJS)
$(LD) -T link.ld -o $# $^
$(SOBJS) : $(SFILES)
$(AS) $(ASFLAGS) $< -o $#
%.o: %.c
#echo Compiling $<...
$(CC) $(CFLAGS) -c -o $# $<
#Clean Script - Should clear out all .o files everywhere and all that.
clean:
-del *.img
-del *.o
-del assembly\*.o
-del core.elf
My main issue with this makefile is that when I modify a header file that one or more C files include, the C files aren't rebuilt. I can fix this quite easily by having all of my header files be dependencies for all of my C files, but that would effectively cause a complete rebuild of the project any time I changed/added a header file, which would not be very graceful.
What I want is for only the C files that include the header file I change to be rebuilt, and for the entire project to be linked again. I can do the linking by causing all header files to be dependencies of the target, but I cannot figure out how to make the C files be invalidated when their included header files are newer.
I've heard that GCC has some commands to make this possible (so the makefile can somehow figure out which files need to be rebuilt) but I can't for the life of me find an actual implementation example to look at. Can someone post a solution that will enable this behavior in a makefile?
EDIT: I should clarify, I'm familiar with the concept of putting the individual targets in and having each target.o require the header files. That requires me to be editing the makefile every time I include a header file somewhere, which is a bit of a pain. I'm looking for a solution that can derive the header file dependencies on its own, which I'm fairly certain I've seen in other projects.
As already pointed out elsewhere on this site, see this page:
Auto-Dependency Generation
In short, gcc can automatically create .d dependency files for you, which are mini makefile fragments containing the dependencies of the .c file you compiled.
Every time you change the .c file and compile it, the .d file will be updated.
Besides adding the -M flag to gcc, you'll need to include the .d files in the makefile (like Chris wrote above).
There are some more complicated issues in the page which are solved using sed, but you can ignore them and do a "make clean" to clear away the .d files whenever make complains about not being able to build a header file that no longer exists.
You could add a 'make depend' command as others have stated but why not get gcc to create dependencies and compile at the same time:
DEPS := $(COBJS:.o=.d)
-include $(DEPS)
%.o: %.c
$(CC) -c $(CFLAGS) -MM -MF $(patsubst %.o,%.d,$#) -o $# $<
The '-MF' parameter specifies a file to store the dependencies in.
The dash at the start of '-include' tells Make to continue when the .d file doesn't exist (e.g. on first compilation).
Note there seems to be a bug in gcc regarding the -o option. If you set the object filename to say obj/_file__c.o then the generated _file_.d will still contain _file_.o, not obj/_file_c.o.
This is equivalent to Chris Dodd's answer, but uses a different naming convention (and coincidentally doesn't require the sed magic. Copied from a later duplicate.
If you are using a GNU compiler, the compiler can assemble a list of dependencies for you. Makefile fragment:
depend: .depend
.depend: $(SOURCES)
rm -f ./.depend
$(CC) $(CFLAGS) -MM $^>>./.depend;
include .depend
There is also the tool makedepend, but I never liked it as much as gcc -MM
You'll have to make individual targets for each C file, and then list the header file as a dependency. You can still use your generic targets, and just place the .h dependencies afterwards, like so:
%.o: %.c
#echo Compiling $<...
$(CC) $(CFLAGS) -c -o $# $<
foo.c: bar.h
# And so on...
Basically, you need to dynamically create the makefile rules to rebuild the object files when the header files change. If you use gcc and gnumake, this is fairly easy; just put something like:
$(OBJDIR)/%.d: %.c
$(CC) -MM -MG $(CPPFLAGS) $< | sed -e 's,^\([^:]*\)\.o[ ]*:,$(#D)/\1.o $(#D)/\1.d:,' >$#
ifneq ($(MAKECMDGOALS),clean)
include $(SRCS:%.c=$(OBJDIR)/%.d)
endif
in your makefile.
Over and above what #mipadi said, you can also explore the use of the '-M' option to generate a record of the dependencies. You might even generate those into a separate file (perhaps 'depend.mk') which you then include in the makefile. Or you can find a 'make depend' rule which edits the makefile with the correct dependencies (Google terms: "do not remove this line" and depend).
Simpler solution: Just use the Makefile to have the .c to .o compilation rule be dependent on the header file(s) and whatever else is relevant in your project as a dependency.
E.g., in the Makefile somewhere:
DEPENDENCIES=mydefs.h yourdefs.h Makefile GameOfThrones.S07E01.mkv
::: (your other Makefile statements like rules
::: for constructing executables or libraries)
# Compile any .c to the corresponding .o file:
%.o: %.c $(DEPENDENCIES)
$(CC) $(CFLAGS) -c -o $# $<
None of the answers worked for me. E.g. Martin Fido's answer suggests gcc can create dependency file, but when I tried that it was generating empty (zero bytes) object files for me without any warnings or errors. It might be a gcc bug. I am on
$ gcc --version gcc (GCC) 4.4.7 20120313 (Red Hat 4.4.7-16)
So here's my complete Makefile that works for me; it's a combination of solutions + something that wasn't mentioned by anyone else (e.g. "suffix replacement rule" specified as .cc.o:):
CC = g++
CFLAGS = -Wall -g -std=c++0x
INCLUDES = -I./includes/
# LFLAGS = -L../lib
# LIBS = -lmylib -lm
# List of all source files
SRCS = main.cc cache.cc
# Object files defined from source files
OBJS = $(SRCS:.cc=.o)
# # define the executable file
MAIN = cache_test
#List of non-file based targets:
.PHONY: depend clean all
## .DEFAULT_GOAL := all
# List of dependencies defined from list of object files
DEPS := $(OBJS:.o=.d)
all: $(MAIN)
-include $(DEPS)
$(MAIN): $(OBJS)
$(CC) $(CFLAGS) $(INCLUDES) -o $(MAIN) $(OBJS) $(LFLAGS) $(LIBS)
#suffix replacement rule for building .o's from .cc's
#build dependency files first, second line actually compiles into .o
.cc.o:
$(CC) $(CFLAGS) $(INCLUDES) -c -MM -MF $(patsubst %.o,%.d,$#) $<
$(CC) $(CFLAGS) $(INCLUDES) -c -o $# $<
clean:
$(RM) *.o *~ $(MAIN) *.d
Notice I used .cc .. The above Makefile is easy to adjust for .c files.
Also notice importance of these two lines :
$(CC) $(CFLAGS) $(INCLUDES) -c -MM -MF $(patsubst %.o,%.d,$#) $<
$(CC) $(CFLAGS) $(INCLUDES) -c -o $# $<
so gcc is called once to build a dependency file first, and then actually compiles a .cc file. And so on for each source file.
I believe the mkdep command is what you want. It actually scans .c files for #include lines and creates a dependency tree for them. I believe Automake/Autoconf projects use this by default.
I keep getting this error and I can't figure out what I am doing wrong. I am using an template so I can get in the dir bin the executable. The dir include the header files. The dir obj for the object files created and the src for the .c files.
My makefile
OBJ_dir = obj
INC_DIR = include
OBJECTS = main.o client.o private.o memory.o process.o proxy.o server.o
main.o = main.h memory-private.h stdio.h stdlib.h string.h syscall.h unistd.h wait.h sysexits.h memory.h
client.o = client.h
private.o = private.h
memory.o = memory.h memory_private.h
process.o = process.h
proxy.o = proxy.h
server.o = server.h
CC = gcc
CFLAGS = -Wall –I $(INC_DIR)
LIBS = -lm
out: $(OBJECTS)
$(CC) $(addprefix $(OBJ_dir)/,$(OBJECTS)) -o bin/out $(LIBS)
%.o: src/%.c $($#)
$(CC) $(CFLAGS) -o $(OBJ_dir)/$# -c $<
clean:
rm –f *.o out
rm –f out
There are many issues here. It's probably a good idea to read at least the first few chapters of the GNU make manual to understand how make and makefiles work.
Take this rule:
out: $(OBJECTS)
$(CC) $(addprefix $(OBJ_dir)/,$(OBJECTS)) -o bin/out $(LIBS)
First, it's not right to list a different target than the file you actually build. Here you told make you'd build a target named out, but your recipe actually builds a target named bin/out. That's wrong.
Second, but similarly, it's not right to have your target depend on one set of prerequisites (the files defined by $(OBJECTS)) but then have the recipe of your rule use a completely different set of prerequisites (by adding a $(OBJ_dir)/ prefix to all the files).
This tells make "please build files main.o, client.o, etc., but what my command will actually use is files obj/main.o, obj/client.o, etc.". It doesn't make sense to tell make to build targets that you aren't going to actually use.
This should be:
bin/out: $(addprefix $(OBJ_dir)/,$(OBJECTS))
$(CC) $^ -o $# $(LIBS)
In general if you ever find yourself writing a recipe where you are modifying the automatic variables like $# or $^ instead of using them as-is, you're almost certainly doing something wrong.
Next your pattern rule has other issues:
%.o: src/%.c $($#)
$(CC) $(CFLAGS) -o $(OBJ_dir)/$# -c $<
First, you cannot use automatic variables like $# in a prerequisite list. Those values are only set when expanding the recipe of a rule. They are not set (empty) when evaluating the prerequisite list. So $($#) expands to the empty string here and does nothing.
Second you have the same problem as above where you are not creating $# you are creating $(OBJ_dir)/$# which is wrong. You should write your rule like this:
$(OBJ_dir)/%.o: src/%.c
$(CC) $(CFLAGS) -o $# -c $<
so that the target lists the file you want to build, and the recipe uses $# without modification.
As for your prerequisites, you should just create them directly rather than trying to use fancy variables (which can't work). As the comment above suggests, just change:
proxy.o = proxy.h
to:
proxy.o : proxy.h
(and all the rest) and it will work. Note, though, that make always builds the first explicit target it sees by default so you may have to re-arrange your makefile a little bit if you want bin/out to be the default target.
I have the following makefile that I use to build a program (a kernel, actually) that I'm working on. Its from scratch and I'm learning about the process, so its not perfect, but I think its powerful enough at this point for my level of experience writing makefiles.
AS = nasm
CC = gcc
LD = ld
TARGET = core
BUILD = build
SOURCES = source
INCLUDE = include
ASM = assembly
VPATH = $(SOURCES)
CFLAGS = -Wall -O -fstrength-reduce -fomit-frame-pointer -finline-functions \
-nostdinc -fno-builtin -I $(INCLUDE)
ASFLAGS = -f elf
#CFILES = core.c consoleio.c system.c
CFILES = $(foreach dir,$(SOURCES),$(notdir $(wildcard $(dir)/*.c)))
SFILES = assembly/start.asm
SOBJS = $(SFILES:.asm=.o)
COBJS = $(CFILES:.c=.o)
OBJS = $(SOBJS) $(COBJS)
build : $(TARGET).img
$(TARGET).img : $(TARGET).elf
c:/python26/python.exe concat.py stage1 stage2 pad.bin core.elf floppy.img
$(TARGET).elf : $(OBJS)
$(LD) -T link.ld -o $# $^
$(SOBJS) : $(SFILES)
$(AS) $(ASFLAGS) $< -o $#
%.o: %.c
#echo Compiling $<...
$(CC) $(CFLAGS) -c -o $# $<
#Clean Script - Should clear out all .o files everywhere and all that.
clean:
-del *.img
-del *.o
-del assembly\*.o
-del core.elf
My main issue with this makefile is that when I modify a header file that one or more C files include, the C files aren't rebuilt. I can fix this quite easily by having all of my header files be dependencies for all of my C files, but that would effectively cause a complete rebuild of the project any time I changed/added a header file, which would not be very graceful.
What I want is for only the C files that include the header file I change to be rebuilt, and for the entire project to be linked again. I can do the linking by causing all header files to be dependencies of the target, but I cannot figure out how to make the C files be invalidated when their included header files are newer.
I've heard that GCC has some commands to make this possible (so the makefile can somehow figure out which files need to be rebuilt) but I can't for the life of me find an actual implementation example to look at. Can someone post a solution that will enable this behavior in a makefile?
EDIT: I should clarify, I'm familiar with the concept of putting the individual targets in and having each target.o require the header files. That requires me to be editing the makefile every time I include a header file somewhere, which is a bit of a pain. I'm looking for a solution that can derive the header file dependencies on its own, which I'm fairly certain I've seen in other projects.
As already pointed out elsewhere on this site, see this page:
Auto-Dependency Generation
In short, gcc can automatically create .d dependency files for you, which are mini makefile fragments containing the dependencies of the .c file you compiled.
Every time you change the .c file and compile it, the .d file will be updated.
Besides adding the -M flag to gcc, you'll need to include the .d files in the makefile (like Chris wrote above).
There are some more complicated issues in the page which are solved using sed, but you can ignore them and do a "make clean" to clear away the .d files whenever make complains about not being able to build a header file that no longer exists.
You could add a 'make depend' command as others have stated but why not get gcc to create dependencies and compile at the same time:
DEPS := $(COBJS:.o=.d)
-include $(DEPS)
%.o: %.c
$(CC) -c $(CFLAGS) -MM -MF $(patsubst %.o,%.d,$#) -o $# $<
The '-MF' parameter specifies a file to store the dependencies in.
The dash at the start of '-include' tells Make to continue when the .d file doesn't exist (e.g. on first compilation).
Note there seems to be a bug in gcc regarding the -o option. If you set the object filename to say obj/_file__c.o then the generated _file_.d will still contain _file_.o, not obj/_file_c.o.
This is equivalent to Chris Dodd's answer, but uses a different naming convention (and coincidentally doesn't require the sed magic. Copied from a later duplicate.
If you are using a GNU compiler, the compiler can assemble a list of dependencies for you. Makefile fragment:
depend: .depend
.depend: $(SOURCES)
rm -f ./.depend
$(CC) $(CFLAGS) -MM $^>>./.depend;
include .depend
There is also the tool makedepend, but I never liked it as much as gcc -MM
You'll have to make individual targets for each C file, and then list the header file as a dependency. You can still use your generic targets, and just place the .h dependencies afterwards, like so:
%.o: %.c
#echo Compiling $<...
$(CC) $(CFLAGS) -c -o $# $<
foo.c: bar.h
# And so on...
Basically, you need to dynamically create the makefile rules to rebuild the object files when the header files change. If you use gcc and gnumake, this is fairly easy; just put something like:
$(OBJDIR)/%.d: %.c
$(CC) -MM -MG $(CPPFLAGS) $< | sed -e 's,^\([^:]*\)\.o[ ]*:,$(#D)/\1.o $(#D)/\1.d:,' >$#
ifneq ($(MAKECMDGOALS),clean)
include $(SRCS:%.c=$(OBJDIR)/%.d)
endif
in your makefile.
Over and above what #mipadi said, you can also explore the use of the '-M' option to generate a record of the dependencies. You might even generate those into a separate file (perhaps 'depend.mk') which you then include in the makefile. Or you can find a 'make depend' rule which edits the makefile with the correct dependencies (Google terms: "do not remove this line" and depend).
Simpler solution: Just use the Makefile to have the .c to .o compilation rule be dependent on the header file(s) and whatever else is relevant in your project as a dependency.
E.g., in the Makefile somewhere:
DEPENDENCIES=mydefs.h yourdefs.h Makefile GameOfThrones.S07E01.mkv
::: (your other Makefile statements like rules
::: for constructing executables or libraries)
# Compile any .c to the corresponding .o file:
%.o: %.c $(DEPENDENCIES)
$(CC) $(CFLAGS) -c -o $# $<
None of the answers worked for me. E.g. Martin Fido's answer suggests gcc can create dependency file, but when I tried that it was generating empty (zero bytes) object files for me without any warnings or errors. It might be a gcc bug. I am on
$ gcc --version gcc (GCC) 4.4.7 20120313 (Red Hat 4.4.7-16)
So here's my complete Makefile that works for me; it's a combination of solutions + something that wasn't mentioned by anyone else (e.g. "suffix replacement rule" specified as .cc.o:):
CC = g++
CFLAGS = -Wall -g -std=c++0x
INCLUDES = -I./includes/
# LFLAGS = -L../lib
# LIBS = -lmylib -lm
# List of all source files
SRCS = main.cc cache.cc
# Object files defined from source files
OBJS = $(SRCS:.cc=.o)
# # define the executable file
MAIN = cache_test
#List of non-file based targets:
.PHONY: depend clean all
## .DEFAULT_GOAL := all
# List of dependencies defined from list of object files
DEPS := $(OBJS:.o=.d)
all: $(MAIN)
-include $(DEPS)
$(MAIN): $(OBJS)
$(CC) $(CFLAGS) $(INCLUDES) -o $(MAIN) $(OBJS) $(LFLAGS) $(LIBS)
#suffix replacement rule for building .o's from .cc's
#build dependency files first, second line actually compiles into .o
.cc.o:
$(CC) $(CFLAGS) $(INCLUDES) -c -MM -MF $(patsubst %.o,%.d,$#) $<
$(CC) $(CFLAGS) $(INCLUDES) -c -o $# $<
clean:
$(RM) *.o *~ $(MAIN) *.d
Notice I used .cc .. The above Makefile is easy to adjust for .c files.
Also notice importance of these two lines :
$(CC) $(CFLAGS) $(INCLUDES) -c -MM -MF $(patsubst %.o,%.d,$#) $<
$(CC) $(CFLAGS) $(INCLUDES) -c -o $# $<
so gcc is called once to build a dependency file first, and then actually compiles a .cc file. And so on for each source file.
I believe the mkdep command is what you want. It actually scans .c files for #include lines and creates a dependency tree for them. I believe Automake/Autoconf projects use this by default.
I have many functions in different files.
eg: OBJ_SRC=sum.c sub.c mul.c div.c remainder.c
When I am creating a library I do like this:
libarithmatic.a: $(OBJ_SRC)
gcc -c $(OBJ_SRC) # creates sum.o sub.o..
ar rcs libarithmatic.a $(OBJS) #<--- problem #OBJS
How to store the output of gcc -c $(OBJ_SRC): add.o sub.o mul.o.. (newly created/updated file names) into OBJS variable?
The usual way is with patsubst
OBJS=$(patsubst %.c,%.o,$(OBJ-SRC))
Now calling gcc as part of the target to build the library is a bad idea. It misses the main point of using make at all as you are asking gcc to blindly recompile all the objects instead of having make find which have changed. The usual rule is:
libarithmatic.a: $(OBJS)
ar rcs libarithmatic.a $(OBJS)
You can put in the pattern rule for compiling the .c files, but if you'd just put in
%.o: %.c
gcc -c $<
you don't have to bother as that is implicit. Well, the default implicit rule is really
%.o: %.c
$(CC) $(CPPFLAGS) $(CFLAGS) -o $# $<
where CC defaults to suitable compiler and you can override it and CPPFLAGS and CFLAGS default to empty and you can set them to whatever flags you want to use for compilation. CPPFLAGS is for both C and C++, CFLAGS is for C only, CXXFLAGS is for C++ only (C++ compiler is CXX).
On a side-note, I'd suggest looking at CMake, which supports generating build files for various platforms, IDEs and the new ultra-fast ninja. The corresponding CMakeLists.txt would be as trivial as
project(arithmatic)
add_library(arithmatic sum.c sub.c mul.c div.c remainder.c)
and making it a shared library as trivial as adding SHARED keyword when you want to.
Note, that the % placeholder does not have to be at the beginning. If you want to put the objects in different directory from the sources, you can write things like
OBJS=$(patsubst src/%.c,obj/%.o,$(SOURCES))
(the sources have to be listed with the directory prefix in this case) or perhaps
OBJS=$(patsubst %.c,.objs/%.o,$(SOURCES))
And you can similarly use the pattern in the rules, so
obj/%.o: src/%.c
mkdir -p obj
$(CC) $(CPPFLAGS) $(CFLAGS) -o $# $<
or
.objs/%.o: %.c
mkdir -p .objs
$(CC) $(CPPFLAGS) $(CFLAGS) -o $# $<
You have to make sure the output directory exists as the compiler won't create it (so I include the mkdir in the rules) and you have to explicitly specify compiler output, because it would create it in current directory otherwise.
I really can't get into makefiles. In previous projects, I hardcoded all compile tasks in the Makefile:
all: compile_a compile_b compile_c
compile_a:
${CC} ${CFLAGS} ${A_SRC} -o ${A_OUT}
and so on.
But as the latest project has more files than every project before, I want to write better make tasks and of course LESS characters as make is not really friendly to my eyes (it makes them suffer)! :-P
What I want:
One task to rule them all (just make projectname or make all, you know?)
One task for every C file to compile (I read something about this %.o: %.c syntax, but didn't really get it)
One task for linking (how to get all .o files and link them without hardcoding each?)
One task for cleaning (oh, i can do this!)
The project structure is:
bin (binary goes here!)
src
some
directories
are
here
I don't know if I need a directory for object files, I put them in ./bin, I think that's good enough, isn't it?
Maybe I just need someone who can explain it with easy words!
EDIT:
As someone pointed out, there's no real question, so here it goes:
how to recursively compile all C files to bin/(filename).o
how to link all .o files in 'bin/' without knowing their names
maybe this helps.
Try this:
CC = gcc
CFLAGS = -c -Wall -g -Os
LD = $(CC)
LDFLAGS = -lfoo
TARGET = MyProject
OBJECTS = $(patsubst %.c, %.o, $(wildcard *.c))
all: $(TARGET)
$(TARGET): $(OBJECTS)
$(LD) -o $# $^ $(LDFLAGS)
# You don't even need to be explicit here,
# compiling C files is handled automagically by Make.
%.o: %.c
$(CC) $(CFLAGS) $^ -o $#
clean:
rm $(TARGET) $(OBJECTS)
I frequently use the wildcard function in combination with the foreach function for something like you want to achieve.
If your sources are in src/ and you want to put the binaries into bin/ the basic construction of my Makefile would look like follows:
SOURCES=$(shell find src -type f -iname '*.c')
OBJECTS=$(foreach x, $(basename $(SOURCES)), $(x).o)
TARGET=bin/MyProject
$(TARGET): $(OBJECTS)
$(CC) $^ -o $#
clean:
rm -f $(TARGET) $(OBJECTS)
I usually take advantage of make's built in implicit rules and predefined variables (Make manual, Chap 10).
without going into specifics of makefiles, use the * to your advantage.
i.e.
compileAll: gcc -c *.c
linkAll: gcc *.o -o output.exe