can't find .so library -l in makefile

Question

I am new to makefiles, I want to make an.so library and use it in main.o file, I want to use the library from the current directory. how can I make this works?

CFLAGS = -Wall -g
CC = g++

all: main.o mylib.so
    $(CC) main.o mylib.so -o runProg

mylib.so : b1.o a1.o head1.h header2.h header3.h
    $(CC) $(CFLAGS) -shared -fPIC -o mylib.so b1.o a1.o

b1.o: b1.cc b1.h
    $(CC) $(CFLAGS) -fPIC b1.cc

a1.o: a1.cc
    $(CC) $(CFLAGS) -fPIC a1.cc

main.o: main.cc 
    $(CC) $(CFLAGS) main.cc -L. -lmylib

error i am getting:

c:/mingw/bin/../lib/gcc/mingw32/6.3.0/../../../../mingw32/bin/ld.exe: cannot find -lmylib
collect2.exe: error: ld returned 1 exit status
makefile:28: recipe for target 'main.o' failed
mingw32-make: *** [main.o] Error 1

any help and correction to make this work is really appreciated!

Answer 1

So a few things wrong. When you are using $(CC) for compilation only, you must specify -c . So

b1.o: b1.cc b1.h
    $(CC) -c $(CFLAGS) -fPIC b1.cc

a1.o: a1.cc
    $(CC) -c $(CFLAGS) -fPIC a1.cc

Going from main.cc to main.o is a compilation step, so doesn't need the shared library (but does need the -c option). So

main.o: main.cc 
    $(CC) -c $(CFLAGS) main.cc

The program linking step does need the library options and should mention the file being produced (rather than all ). So

runProg: main.o mylib.so
    $(CC) main.o -o runProg -L. -lmylib

Haven't checked anything, but hopefully that helps. No doubt if anything is wrong it will be corrected.