Geting source code structure in Makefile - c

Question

I'm working on a C project, and I decided to put the source code and its objects in different directories. The root directory has something like that:
SmartC ▶ tree -L 1
.
├── built
├── doc
├── Makefile
├── README.md
├── src
├── tests
└── trash
So, inside both src and built directories, I put two others Makefiles to do the compile and link jobs.
The src directory (where I put the source code) has the following structure:
src
├── graph.c
├── graph.h
├── list.c
├── list.h
├── main.c
├── Makefile
├── node.c
├── node.h
├── tree.c
├── tree.h
└── types
├── complex.c
├── complex.h
├── matrix.c
└── matrix.h
and the built has the same structure, but it is intended to store all objects made by compilation.
My question is about my src/Makefile:
BINDIR = ../built/src
CC = gcc
CFLAGS = -g -Wall -O3
OBJECTS = \
$(BINDIR)/main.o \
$(BINDIR)/node.o \
$(BINDIR)/list.o \
$(BINDIR)/graph.o \
$(BINDIR)/tree.o \
$(BINDIR)/types/complex.o \
$(BINDIR)/types/matrix.o \
compile: $(OBJECTS)
$(BINDIR)/%.o: %.c
$(CC) -c $< -o $# $(CFLAGS)
This Makefile creates all the objects of the source code, inside src directory, and move them to built/src. But, every time I create a new source code file (*.c), I have to put the name of its object in this makefile, so it can be compiled. I'd like to do an automatic search, inside the src directory, and fill the "OBJECTS" variable with this search.
Is anyone has some idea of how to accomplish this? I mean, automatic search for source code inside an specific directory?
I even accept any other strategy rather than what I'm making.
=========== Answer ===============
I got the tip (in comments) about wildcards. So I did. Here is the solution I found.
src/Makefile
BINDIR = ../built/src
CC = gcc
CFLAGS = -g -Wall -O3
OBJECTS := $(patsubst %.c,$(BINDIR)/%.o,$(wildcard *.c */*.c))
compile: $(OBJECTS)
$(BINDIR)/%.o: %.c
$(CC) -c $< -o $# $(CFLAGS)

Answer 1

EDIT [Solved]
I like to do the following.
Create Variables to Each Directory of the Project
SRCDIR = src
OBJDIR = obj
LIBDIR = lib
DOCDIR = doc
HDRDIR = include
CFLAGS = -g -Wall -O3
Get Only the Internal Structure of SRCDIR Recursively
STRUCTURE := $(shell find $(SRCDIR) -type d)
Get All Files inside the STRUCTURE Variable
CODEFILES := $(addsuffix /*,$(STRUCTURE))
CODEFILES := $(wildcard $(CODEFILES))
Filter Out Only Specific Files
# Filter Only Specific Files
SRCFILES := $(filter %.c,$(CODEFILES))
HDRFILES := $(filter %.h,$(CODEFILES))
OBJFILES := $(subst $(SRCDIR),$(OBJDIR),$(SRCFILES:%.c=%.o))
# Filter Out Function main for Libraries
LIBDEPS := $(filter-out $(OBJDIR)/main.o,$(OBJFILES))
Now it is Time to create the Rules
compile: $(OBJFILES)
$(OBJDIR)/%.o: $(addprefix $(SRCDIR)/,%.c %.h)
$(CC) -c $< -o $# $(CFLAGS)
With this approach, you can see that I'm using the STRUCTURE variable only to get the files inside the SRCDIR directory, but it can be used for others purposes as well, like mirror the SRCDIR inside OBJDIR once STRUCTURE stores only the internal sub-directories. It is quite useful after clean operations like:
clean:
-rm -r $(OBJDIR)/*
NOTE: The compile rule only works well if for each *.c there is the corresponding *.h file (with the same base name, I mean).