Re: gcc -M deficiencies; workaround?

[gk]

At 04:58 PM 1/15/2003 -0500, Paul D. Smith wrote:
> %% gk <address@hidden> writes:
>
>   g> Since gcc -M only returns prerequisite files included with #include
>   g> directive, it cannot list prerequisite files accessed by fopen(),
>   g> etc.
>
> Why in the world would you want to recompile a C file because a file that
> it fopen()s had changed?

Good question. I guess I shouldn't have said 'gcc -M deficiencies'
I didn't mean to imply that gcc -M SHOULD include any other files, just 
that there is a need of some way to determine additional prerequisites of 
the OUTPUT sometimes.

Sometimes if foo.o is part of a chain of makefile rules, the output target 
that depends on foo.o needs to know what files the OUTPUT of foo.o depends on.

Strictly speaking foo.o does not depend on a file opened by fopen(), but 
the OUTPUT that is produced by executing foo.o may depend on the files 
used, which could be determinable automatically if foo.c 'registered' the 
files it's output depends on, as in my PHP example in previous post.

I think perhaps the answer to my question is to build the functionality I'm 
seeking into foo.o
But this imposes requires foo.c to process options, which isn't always what 
I want:
$foo.o -M
foo.txt

Simple example:
'foo.c' reads a file 'foo.txt' and writes the contents to /dev/stdout
'foo.o' outputs the contents of file: 'foo.txt'

# makefile
.PHONY: result
CC=gcc

# Command to generate a list of dependencies from a source file (including 
the source file)
# $(1) - source file
# remove the leading 'outputFile.o :'
define prerequisites
$(filter-out \,$(patsubst %:,,$(shell $(CC) -M $(1))))
endef

# IS THE THE ANSWER?
# $(1) - binary file
define get_prerequisites
$(1) -M
endef

foo.result: foo.o $(call get_prerequisites,foo.o)
        @$< > $@
foo.o: $(call prerequisites,foo.c)
        $(CC) -o $@ $<
# eof



- Greg Keraunen
http://www.xmake.org
http://www.xmlmake.com