Create directories using make file

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given that you're a newbie, I'd say don't try to do this yet. it's definitely possible, but will needlessly complicate your Makefile. stick to the simple ways until you're more comfortable with make.

that said, one way to build in a directory different from the source directory is VPATH; i prefer pattern rules

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最佳答案

This would do it - assuming a Unix-like environment.

MKDIR_P = mkdir -p


.PHONY: directories


all: directories program


directories: ${OUT_DIR}


${OUT_DIR}:
${MKDIR_P} ${OUT_DIR}

This would have to be run in the top-level directory - or the definition of ${OUT_DIR} would have to be correct relative to where it is run. Of course, if you follow the edicts of Peter Miller's "Recursive Make Considered Harmful" paper, then you'll be running make in the top-level directory anyway.

I'm playing with this (RMCH) at the moment. It needed a bit of adaptation to the suite of software that I am using as a test ground. The suite has a dozen separate programs built with source spread across 15 directories, some of it shared. But with a bit of care, it can be done. OTOH, it might not be appropriate for a newbie.

As noted in the comments, listing the 'mkdir' command as the action for 'directories' is wrong. As also noted in the comments, there are other ways to fix the 'do not know how to make output/debug' error that results. One is to remove the dependency on the the 'directories' line. This works because 'mkdir -p' does not generate errors if all the directories it is asked to create already exist. The other is the mechanism shown, which will only attempt to create the directory if it does not exist. The 'as amended' version is what I had in mind last night - but both techniques work (and both have problems if output/debug exists but is a file rather than a directory).

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In my opinion, directories should not be considered targets of your makefile, either in technical or in design sense. You should create files and if a file creation needs a new directory then quietly create the directory within the rule for the relevant file.

If you're targeting a usual or "patterned" file, just use make's internal variable $(@D), that means "the directory the current target resides in" (cmp. with $@ for the target). For example,

$(OUT_O_DIR)/%.o: %.cpp
@mkdir -p $(@D)
@$(CC) -c $< -o $@


title: $(OBJS)

Then, you're effectively doing the same: create directories for all $(OBJS), but you'll do it in a less complicated way.

The same policy (files are targets, directories never are) is used in various applications. For example, git revision control system doesn't store directories.

Note: If you're going to use it, it might be useful to introduce a convenience variable and utilize make's expansion rules.

dir_guard=@mkdir -p $(@D)


$(OUT_O_DIR)/%.o: %.cpp
$(dir_guard)
@$(CC) -c $< -o $@


$(OUT_O_DIR_DEBUG)/%.o: %.cpp
$(dir_guard)
@$(CC) -g -c $< -o $@


title: $(OBJS)

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I've just come up with a fairly reasonable solution that lets you define the files to build and have directories be automatically created. First, define a variable ALL_TARGET_FILES that holds the file name of every file that your makefile will be build. Then use the following code:

define depend_on_dir
$(1): | $(dir $(1))


ifndef $(dir $(1))_DIRECTORY_RULE_IS_DEFINED
$(dir $(1)):
mkdir -p $$@


$(dir $(1))_DIRECTORY_RULE_IS_DEFINED := 1
endif
endef


$(foreach file,$(ALL_TARGET_FILES),$(eval $(call depend_on_dir,$(file))))

Here's how it works. I define a function depend_on_dir which takes a file name and generates a rule that makes the file depend on the directory that contains it and then defines a rule to create that directory if necessary. Then I use foreach to call this function on each file name and eval the result.

Note that you'll need a version of GNU make that supports eval, which I think is versions 3.81 and higher.

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All solutions including the accepted one have some issues as stated in their respective comments. The accepted answer by @jonathan-leffler is already quite good but does not take into effect that prerequisites are not necessarily to be built in order (during make -j for example). However simply moving the directories prerequisite from all to program provokes rebuilds on every run AFAICT. The following solution does not have that problem and AFAICS works as intended.

MKDIR_P := mkdir -p
OUT_DIR := build


.PHONY: directories all clean


all: $(OUT_DIR)/program


directories: $(OUT_DIR)


$(OUT_DIR):
${MKDIR_P} $(OUT_DIR)


$(OUT_DIR)/program: | directories
touch $(OUT_DIR)/program


clean:
rm -rf $(OUT_DIR)

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OS independence is critical for me, so mkdir -p is not an option. I created this series of functions that use eval to create directory targets with the prerequisite on the parent directory. This has the benefit that make -j 2 will work without issue since the dependencies are correctly determined.

# convenience function for getting parent directory, will eventually return ./
#     $(call get_parent_dir,somewhere/on/earth/) -> somewhere/on/
get_parent_dir=$(dir $(patsubst %/,%,$1))


# function to create directory targets.
# All directories have order-only-prerequisites on their parent directories
# https://www.gnu.org/software/make/manual/html_node/Prerequisite-Types.html#Prerequisite-Types
TARGET_DIRS:=
define make_dirs_recursively
TARGET_DIRS+=$1
$1: | $(if $(subst ./,,$(call get_parent_dir,$1)),$(call get_parent_dir,$1))
mkdir $1
endef


# function to recursively get all directories
#     $(call get_all_dirs,things/and/places/) -> things/ things/and/ things/and/places/
#     $(call get_all_dirs,things/and/places) -> things/ things/and/
get_all_dirs=$(if $(subst ./,,$(dir $1)),$(call get_all_dirs,$(call get_parent_dir,$1)) $1)


# function to turn all targets into directories
#     $(call get_all_target_dirs,obj/a.o obj/three/b.o) -> obj/ obj/three/
get_all_target_dirs=$(sort $(foreach target,$1,$(call get_all_dirs,$(dir $(target)))))


# create target dirs
create_dirs=$(foreach dirname,$(call get_all_target_dirs,$1),$(eval $(call make_dirs_recursively,$(dirname))))


TARGETS := w/h/a/t/e/v/e/r/things.dat w/h/a/t/things.dat


all: $(TARGETS)


# this must be placed after your .DEFAULT_GOAL, or you can manually state what it is
# https://www.gnu.org/software/make/manual/html_node/Special-Variables.html
$(call create_dirs,$(TARGETS))


# $(TARGET_DIRS) needs to be an order-only-prerequisite
w/h/a/t/e/v/e/r/things.dat: w/h/a/t/things.dat | $(TARGET_DIRS)
echo whatever happens > $@


w/h/a/t/things.dat: | $(TARGET_DIRS)
echo whatever happens > $@

For example, running the above will create:

$ make
mkdir w/
mkdir w/h/
mkdir w/h/a/
mkdir w/h/a/t/
mkdir w/h/a/t/e/
mkdir w/h/a/t/e/v/
mkdir w/h/a/t/e/v/e/
mkdir w/h/a/t/e/v/e/r/
echo whatever happens > w/h/a/t/things.dat
echo whatever happens > w/h/a/t/e/v/e/r/things.dat

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Or, KISS.

DIRS=build build/bins


...


$(shell mkdir -p $(DIRS))

This will create all the directories after the Makefile is parsed.

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make in, and off itself, handles directory targets just the same as file targets. So, it's easy to write rules like this:

outDir/someTarget: Makefile outDir
touch outDir/someTarget


outDir:
mkdir -p outDir

The only problem with that is, that the directories timestamp depends on what is done to the files inside. For the rules above, this leads to the following result:

$ make
mkdir -p outDir
touch outDir/someTarget
$ make
touch outDir/someTarget
$ make
touch outDir/someTarget
$ make
touch outDir/someTarget

This is most definitely not what you want. Whenever you touch the file, you also touch the directory. And since the file depends on the directory, the file consequently appears to be out of date, forcing it to be rebuilt.

However, you can easily break this loop by telling make to ignore the timestamp of the directory. This is done by declaring the directory as an order-only prerequsite:

# The pipe symbol tells make that the following prerequisites are order-only
#                           |
#                           v
outDir/someTarget: Makefile | outDir
touch outDir/someTarget


outDir:
mkdir -p outDir

This correctly yields:

$ make
mkdir -p outDir
touch outDir/someTarget
$ make
make: 'outDir/someTarget' is up to date.

TL;DR:

Write a rule to create the directory:

$(OUT_DIR):
mkdir -p $(OUT_DIR)

And have the targets for the stuff inside depend on the directory order-only:

$(OUT_DIR)/someTarget: ... | $(OUT_DIR)

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See https://www.oreilly.com/library/view/managing-projects-with/0596006101/ch12.html

REQUIRED_DIRS = ...
_MKDIRS := $(shell for d in $(REQUIRED_DIRS); \
do                               \
[[ -d $$d ]] || mkdir -p $$d;  \
done)


$(objects) : $(sources)

As I use Ubuntu, I also needed add this at the top of my Makefile:

SHELL := /bin/bash # Use bash syntax

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I use the makefiles in windows environment and my simple solution is as follows,

Create a target makedir and add it as a prerequisites to where ever it is required.

# Default goal
all: gccversion makedir build finalize list sizeafter completed

The makedir target is (applicable only in windows environment)

makedir:
@IF NOT EXIST $(subst /,\,$(BUILD_DIR)) mkdir $(subst /,\,$(BUILD_DIR)) 2> NULL
@IF NOT EXIST $(subst /,\,$(OUTPUT_DIR)) mkdir $(subst /,\,$(OUTPUT_DIR)) 2> NULL
@IF NOT EXIST $(subst /,\,$(DEP_DIR)) mkdir $(subst /,\,$(DEP_DIR)) 2> NUL
@IF NOT EXIST $(subst /,\,$(OBJ_DIR)) mkdir $(subst /,\,$(OBJ_DIR)) 2> NUL

$(subst /,\,$(BUILD_DIR)) converts the directory separator / to \ and mkdir $(subst /,\,$(BUILD_DIR)) 2> NUL redirects the error if any.

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src_dir := src
obj_dir := obj
build_dir := build


dirs := $(src_dir) $(obj_dir) $(build_dir)   # new variable




all: $(dirs) $(other_dependencies)           # added dependency (*before* any others)


$(dirs):                                     # rule which makes missing directories
mkdir $@

Won't clutter your terminal with "cannot create directory" error messages. If the directories exist, they don't need to be built.
Works like any other dependency, only requires one rule and one variable.