Makefile_4_macro

# Makefile:

# build shared library with -fPIC, -shared
CFLAGS   = # -g # -O3 # -fPIC  # CXXFLAGS for .cpp
LDFLAGS  = # -L../foo -Wl,-rpath,../foo # -shared
LDLIBS   = # -lhello
CPPFLAGS = -MMD -MP # -I../hello
#CC      = $(CXX)  # link with CXX for .cpp

all: main

# turn off assert() with NDEBUG
ifdef NDEBUG
CPPFLAGS += -DNDEBUG
CFLAGS += -O3
else
CFLAGS += -g
endif

# target name is basename of one of the source files
main : $(patsubst %.c,%.o,$(wildcard *.c))  # .cpp
-include *.d
clean : ; -rm -fr *.o *.d
.PHONY : clean

----

//main.c

#include <stdio.h>
#include <assert.h>
#include "hello.h"

int main(){
#ifndef NDEBUG
    printf("no def\n");
#else
    printf("yes def\n");
#endif
    int i = 0;
    assert(i);
    hello();
}

----

$ make NDEBUG=1
cc -O3 -DNDEBUG -MMD -MP   -c -o main.o main.c
cc   main.o hello.o   -o main
$

$ make
cc -g -MMD -MP   -c -o main.o main.c
cc   main.o hello.o   -o main
$