How to generate object files in the build directory?

I am currently working on a C project to implement a Linux userspace application. I wrote this Makefile, which allows me to compile :

PROJ_DIR := ../
SRC_DIR := $(PROJ_DIR)/src
BUILD_DIR := $(PROJ_DIR)/build

# define the executable file
TARGET := tcp_proxy

# include paths list
INC_DIRS := $(SRC_DIR)
INC_DIRS += $(SRC_DIR)/rpmsg
INC_DIRS += $(SRC_DIR)/rpmsg/rx
INC_DIRS += $(SRC_DIR)/rpmsg/tx
INC_DIRS += $(SRC_DIR)/tcp
INC_DIRS += $(SRC_DIR)/tcp/rx
INC_DIRS += $(SRC_DIR)/tcp/tx

INC_FLAGS := $(addprefix -I,$(INC_DIRS))

# source file list
SRCS := $(shell find $(SRC_DIR) -name *.c)

# object file list
OBJS := $(SRCS:.c=.o)

LDFLAGS := -pthread

all: tcp_proxy

tcp_proxy: $(OBJS)
    $(CC) $(CFLAGS) $(INC_FLAGS) -o $(TARGET) $(OBJS) $(LDFLAGS)

%.o: %.c
    $(CC) $(CFLAGS) $(INC_FLAGS) -c $< -o $@

.PHONY: clean

clean:
    $(RM) *.o *~ $(TARGET)

However, the object files are generated in the same place as the source files. So I would like to know how to duplicate the folders under "src" in a "build" directory and generate inside this directory the object files and the executable.

I would also like, when I do a make clean, to be able to delete all the object files and the executable.

My project :

Searching would definitely find you a lot of examples and information on this.

First tell make what objects you want to build; change your setting of OBJS to this:

# object file list
OBJS := $(SRCS:$(SRC_DIR)/%.c=$(OBJ_DIR)/%.o)

Then tell make how to build it; change your pattern rule for building objects to this:

$(OBJ_DIR)/%.o: $(SRC_DIR)/%.c
        @mkdir -p $(@D)
        $(CC) $(CFLAGS) $(INC_FLAGS) -c $< -o $@