Re: [gentoo-amd64] Re: How does gcc find a library?

[Mark Knecht]

On Sun, May 17, 2009 at 1:13 PM, Duncan <1i5t5.duncan@×××.net> wrote:
> Mark Knecht <markknecht@×××××.com> posted
> 5bdc1c8b0905170849j3e0198ebrf29bc2042dda7ee4@××××××××××.com, excerpted
> below, on  Sun, 17 May 2009 08:49:13 -0700:
>
>> Hi,
>>    I'm trying to compile a new piece of software for MythTV hardware
>> support that's not in portage. I'm not a programmer so I'm woefully
>> uneducated in this area but how does gcc find a library that a piece of
>> code is requiring?
>
> Well, I'm not a programmer either, but I think I understand a bit about
> this just from troubleshooting various ebuilds over time.  YMMV, but the
> below is what I'd try.
>
> gcc looks in various standard system locations (/usr/include, among
> others) automatically for the header files, which tell it the interfaces
> the library supplies.  The interfaces consist of the the functions, etc,
> along with the parameters they take, their orders and their types (int,
> string pointer, whatever).
>
> For header files not found in the standard locations and not in the
> working dir that's being compiled, gcc has the -I<includedir> parameter,
> among others.
>
> Then for linking, there's  -L<linkdir>, if you find you need it later.
>
>>    My code setup is this:
>>
>> /home/mark/scte65scan-0.2
>> /home/mark/scte65scan-0.2/libhdhomerun
>
>> The code all exists in the scte65scan directory. The required library is
>> in libhdhomerun.
>>
>>    When I attempt to build the code I get the error message:
>>
>> mark@Sector9 ~/scte65scan-0.2 $ make -f Makefile.hdhr cc -O2 -DHDHR -c
>> tunerdmx.c -o tunerdmx.o tunerdmx.c:39:23: error: hdhomerun.h: No such
>> file or directory
>
>>    So it seems it cannot find the library because hdhomerun.h is in
>> the libhdhomerun diectory:
>
>>    The tunerdmx.c program has an include for hdhomerun:
>>
>> #ifdef HDHR
>> #include "hdhomerun.h"
>>
>> which is what I guess is kicking off the problem. The makefile looks
>> like this:
>>
>> mark@Sector9 ~/scte65scan-0.2 $ cat Makefile.hdhr
>> HDHR_DIR=./libhdhomerun
>
> That part looks right, since it's a subdir, and the (snipped) LIBOBJS
> point into it as expected.
>
>> CFLAGS += -O2 -DHDHR
>> LDFLAGS += -lpthread
>
>>    So, how do I tell gcc that the library is here so it can build it?
>
> Add to that CFLAGS line: -I./libhdhomerun .  See if that helps.  You can
> try the absolute form too (/home/mark...) but that can cause problems if
> things are moved around, later.  The relative form should help avoid
> those problems.
>
> If you later get hungup in linking, there's the -L<dir> parameter for
> that, too, but I'd not add it until it looks like it's needing it.
>
> As I said above, this is troubleshooting level knowledge.  Try it and see
> if it works more than really understanding the full implications, tho I
> believe I understand why it /should/ work, as explained above -- you're
> simply pointing gcc at the right dirs.
>
> --
> Duncan - List replies preferred.   No HTML msgs.
> "Every nonfree program has a lord, a master --
> and if you use the program, he is your master."  Richard Stallman
>

Thanks Duncan,
   I think it's turning out that this code has not actually been
debugged and the errors are really in the program's code itself. I've
managed to get a few of the simple typo's debugged but there are still
some problems that the developer is going to have to deal with as they
are way beyond me.

   I found that the inclusion of the libhdhomerun stuff could be
accomplished in the makefile by changing the CFLAGS line to include
it::

CFLAGS += -I libhdhomerun -O2 -DHDHR

   This still leaves me with a few problems so it's now a matter of
waiting on the developer.

Thanks again,
Mark