Question

I would like to compile .c files to a .so (shared library).
And I don’t understand why, I have that makefile that makes me an error:

LIB = libmy.so

SRC =   lib.c

CC = gcc

OBJ = $(CC) -c -fPIC $(SRC)

all: $(LIB)

re: fclean all

$(LIB): $(OBJ)
        $(CC) -shared -fPIC $(OBJ) -o $(LIB)

clean:
        $(RM) $(OBJ)

fclean: clean
        $(RM) $(LIB)

Thanks in advance for helping.

Answer 1

The problem is in the following line:

$(LIB): $(OBJ)

When expanded this becomes:

libmy.so : gcc -c -fPIC lib.c

Hence the error.

What you probably wanted was :

OBJ = lib.o

To save you having to manually convert all .c source files to .o you can use a rule like this instead of OBJ = lib.o:

OBJ = $(SRC:%.c=%.o)

This creates a variable OBJ containing a list of all the files in SRC with any .c extension changed to .o. eg. If we had SRC = foo.c bar.c then the rule above would automatically expand to:

OBJ = foo.o bar.o