Its been a bad day for coding. Fixed one problem by writing debug code
deleted debug code and problem is back.

But that's not the issue. This issues is conceptually simple.

I want to use a library. specifically the libiw library

I install the library using apt-get install libiw-dev

I include the file <iwlib.h>

The source code compiles fine, so its found iwlib.h Or at least I assume
so.
When I try to link with -liw though, it simple barfs on any reference to
the library.

I found libiw.so, and it contains all the right symbols.

gcc doesn't say it cannot find the libary, only that it *cannot match
the symbols*.

Specifically

gcc -liw -o scan scan.o
/usr/bin/ld: scan.o: in function `main':
scan.c:(.text+0x1f): undefined reference to `iw_sockets_open'
/usr/bin/ld: scan.c:(.text+0x40): undefined reference to `iw_get_range_info'
/usr/bin/ld: scan.c:(.text+0x7f): undefined reference to `iw_scan'
collect2: error: ld returned 1 exit status

I have never seen this behaviour before.
Any clues?

--
Outside of a dog, a book is a man's best friend. Inside of a dog it's
too dark to read.

Groucho Marx

On Sun, 6 Aug 2023 15:54:00 +0100, The Natural Philosopher wrote:

> The source code compiles fine, so its found iwlib.h Or at least I assume
> so.
> When I try to link with -liw though, it simple barfs on any reference to
> the library.
>
> I found libiw.so, and it contains all the right symbols.
>
> gcc doesn't say it cannot find the libary, only that it *cannot match
> the symbols*.
>
> Specifically
>
> gcc -liw -o scan scan.o /usr/bin/ld: scan.o: in function `main':
> scan.c:(.text+0x1f): undefined reference to `iw_sockets_open'
> /usr/bin/ld: scan.c:(.text+0x40): undefined reference to
> `iw_get_range_info'
> /usr/bin/ld: scan.c:(.text+0x7f): undefined reference to `iw_scan'
> collect2: error: ld returned 1 exit status
>
> I have never seen this behaviour before.
> Any clues?

Anything wrong with the contents of the iwlib.h file? I assume it was
replaced correctly by the update?

--

Martin | martin at
Gregorie | gregorie dot org

On 06/08/2023 15:54, The Natural Philosopher wrote:

> I have never seen this behaviour before.
> Any clues?

Does it need to pick up .so files from LD_LIBRARY_PATH ?

The Natural Philosopher <tnp@invalid.invalid> writes:
> gcc -liw -o scan scan.o
> /usr/bin/ld: scan.o: in function `main':
> scan.c:(.text+0x1f): undefined reference to `iw_sockets_open'
> /usr/bin/ld: scan.c:(.text+0x40): undefined reference to `iw_get_range_info'
> /usr/bin/ld: scan.c:(.text+0x7f): undefined reference to `iw_scan'
> collect2: error: ld returned 1 exit status
>
> I have never seen this behaviour before.
> Any clues?

The library needs to be listed after the object files that depend on it,
not before.

https://gcc.gnu.org/onlinedocs/gcc/Link-Options.html:

It makes a difference where in the command you write this option; the
linker searches and processes libraries and object files in the order
they are specified. Thus, ‘foo.o -lz bar.o’ searches library ‘z’ after
file foo.o but before bar.o. If bar.o refers to functions in ‘z’,
those functions may not be loaded.

--
https://www.greenend.org.uk/rjk/

On 06/08/2023 16:18, Martin Gregorie wrote:
> On Sun, 6 Aug 2023 15:54:00 +0100, The Natural Philosopher wrote:
>
>> The source code compiles fine, so its found iwlib.h Or at least I assume
>> so.
>> When I try to link with -liw though, it simple barfs on any reference to
>> the library.
>>
>> I found libiw.so, and it contains all the right symbols.
>>
>> gcc doesn't say it cannot find the libary, only that it *cannot match
>> the symbols*.
>>
>> Specifically
>>
>> gcc -liw -o scan scan.o /usr/bin/ld: scan.o: in function `main':
>> scan.c:(.text+0x1f): undefined reference to `iw_sockets_open'
>> /usr/bin/ld: scan.c:(.text+0x40): undefined reference to
>> `iw_get_range_info'
>> /usr/bin/ld: scan.c:(.text+0x7f): undefined reference to `iw_scan'
>> collect2: error: ld returned 1 exit status
>>
>> I have never seen this behaviour before.
>> Any clues?
>
> Anything wrong with the contents of the iwlib.h file? I assume it was
> replaced correctly by the update?
>
>
>
As with all these things it is complex, but looks healthy enough.
The compiler didnt barf

--
Climate Change: Socialism wearing a lab coat.

On 06/08/2023 16:40, Andy Burns wrote:
> On 06/08/2023 15:54, The Natural Philosopher wrote:
>
>> I have never seen this behaviour before.
>> Any clues?
>
>
> Does it need to pick up .so files from LD_LIBRARY_PATH ?
>
That is the strange thing. I tried introducing a random library to the
command, , and ld says 'cant find file' so it would seem to be finding
the .so file OK

--
Climate Change: Socialism wearing a lab coat.

On 06/08/2023 17:13, Richard Kettlewell wrote:
> The library needs to be listed after the object files that depend on it,
> not before.

Ah. That seems to have fixed it, thanks.

Code doesn't work very well, but it does link ;)

--
Those who want slavery should have the grace to name it by its proper
name. They must face the full meaning of that which they are advocating
or condoning; the full, exact, specific meaning of collectivism, of its
logical implications, of the principles upon which it is based, and of
the ultimate consequences to which these principles will lead. They must
face it, then decide whether this is what they want or not.

Ayn Rand.