Question

I tried the following code tree. If I put the header file hello.h into the “inc” archive, and use the MM option my system reported that hello.h cannot be found even I add a vpath command in my makefile. If I move the hello.h back to the same directory of hello.c, gcc -MM works fine and listed the dependence file successfully.

How can I make the gcc know where to find the header file automatically? The following is the code tree, and “hello.h” is placed in archive “inc”

    total 12
    -rw-r--r-- 1 root root  101 Jun 22 14:13 hello.c
    drwxr-xr-x 2 root root 4096 Jun 22 14:14 inc
    -rw-r--r-- 1 root root  139 Jun 22 14:18 makefile

The following is my makefile content:

vpath %.h /home/tempcode/inc

hello: hello.o
    gcc -o hello hello.o

hello.o: hello.c hello.h
    gcc -c hello.c

debug:
    gcc -MM hello.c

It makes me puzzled that if I run gcc directly like this, it works. does this mean VPATH or vpath do not help gcc finding the include path ? If so, I guess vpath variable only helps ‘make’ with finding the header file but not helping gcc, am I right?

    [root@localhost tempcode]# gcc -MM -I/home/tempcode/inc hello.c
    hello.o: hello.c /home/tempcode/inc/hello.h

Answer 1

does this mean VPATH or vpath do not help gcc finding the include path ? If so, I guess vpath variable only helps ‘make’ with finding the header file but not helping gcc, am I right?

That is correct. You should set the CFLAGS variable to do what you want. Make automatically includes CFLAGS when compiling C files. (CXXFLAGS for C++.) In your case, you’ll need to add it to make .d files. I usually do something like this:

INCLUDES = -I/home/tempcode/inc
CFLAGS += $(INCLUDES)
CXXFLAGS += $(INCLUDES)

debug:
    gcc -MM $(CFLAGS) hello.c