Prob with linking in gcc!

[abhishek2301]

Hello,

I am stuck with a problem to link static libraries with gcc.
There is no problem with source files since I am able to compile in a machine where the static library is installed.
I am compiling with the following:

:~/Emotion/pjproject-1.0.3/third_party 157% gcc -Wall -I/portaudio/include -o rec patest_record.c -L./lib -lportaudio-x86_64-unknown-linux-gnu

My current path is: ~/Emotion/pjproject-1.0.3/third_party 
Required header file path is: ~/Emotion/pjproject-1.0.3/third_party/portaudio/include/portaudio.h
Static Library path is: ~/Emotion/pjproject-1.0.3/third_party/lib/libportaudio-x86_64-unknown-linux-gnu.a

I don't know where I am committing mistake but I get a loads of undefined reference errors.
I am producing the end part of them:
************************************************** ************************************************** ****

pa_unix_oss.c:(.text+0x1d60): undefined reference to `__pthread_unregister_cancel'
./lib/libportaudio-x86_64-unknown-linux-gnu.a(pa_unix_oss.o): In function `PaOssStream_Terminate':
pa_unix_oss.c:(.text+0x1fb4): undefined reference to `sem_destroy'
./lib/libportaudio-x86_64-unknown-linux-gnu.a(pa_unix_oss.o): In function `OpenStream':
pa_unix_oss.c:(.text+0x2bc6): undefined reference to `sem_init'
pa_unix_oss.c:(.text+0x2d45): undefined reference to `ceil'
collect2: ld returned 1 exit status

************************************************** ************************************************** ***

Pls help me to resove this issue!
Thanks,
Abhishek

[JohnGraham]

PortAudio also needs to be linked against a pthread library (with -lpthread or just -pthread).

Ideally, you should find the portaudio.pc file (in ${prefix}/lib/pkgconfig/portaudio.pc, where ${prefix} is whatever prefix you passed to the configure script). Add something like:

`pkg-config /path/to/portaudio/install/lib/pkgconfig/portaudio.pc --libs`

To your command-line when you link and it should give you all the dependencies it needs.

(You can also use --cflags instead of --libs to get the options it wants for the compiler.)

[abhishek2301]

Thanks for your reply. I understand that it can be done through pkg-config.
But, I have another query.
Using the following :
************************************************** *************************

abhat002@shetland:~/third_party 167% gcc -Wall -I/portaudio/include/ -o
rec2 patest_record.c lib/libportaudio-x86_64-unknown-linux-gnu.a -lpthread
-lrt -lasound -lm

************************************************** *************************
compiles fine and the binary runs perfectly.Whereas the following:
************************************************** *************************

abhat002@shetland:~/third_party 169% gcc -Wall -I/portaudio/include/ -o
rec2 patest_record.c -L./lib -lportaudio-x86_64-unknown-linux-gnu
-lpthread -lrt -lasound -lm
./lib/libasound.a(dlmisc.o): In function `snd_dlsym_verify':
(.text+0x1df): undefined reference to `dlsym'
./lib/libasound.a(dlmisc.o): In function `snd_dlsym':
(.text+0x257): undefined reference to `dlsym'
./lib/libasound.a(dlmisc.o): In function `snd_dlclose':
(.text+0x2ba): undefined reference to `dlclose'
./lib/libasound.a(dlmisc.o): In function `snd_dlopen':
(.text+0x346): undefined reference to `dlopen'
collect2: ld returned 1 exit status
abhat002@shetland:~/third_party 170%

************************************************** *************************
The only difference in the second is in specifying path through -L flag
and so why does it fail to compile though I am using the same static
libraries!
I am not very clear in understanding the exact linking process in gcc.

Thanks!

[JohnGraham]

abhat002@shetland:~/third_party 167% gcc -Wall -I/portaudio/include/ -o
rec2 patest_record.c lib/libportaudio-x86_64-unknown-linux-gnu.a -lpthread
-lrt -lasound -lm

abhat002@shetland:~/third_party 169% gcc -Wall -I/portaudio/include/ -o
rec2 patest_record.c -L./lib -lportaudio-x86_64-unknown-linux-gnu
-lpthread -lrt -lasound -lm

The difference is that in the first one, you're explicitly telling the compiler to link-in lib/libportaudio-x86_64-unknown-linux-gnu.a. In the second one, you're using -L./lib to tell it to look in ./lib for libraries, and -lportaudio-x86_64-unknown-linux-gnu to tell it to look for portaudio-x86_64-unknown-linux-gnu somehow.

In the second case, it has probably spotted (correct me if I'm wrong) a file called ./lib/libportaudio-x86_64-unknown-linux-gnu.so, which is a shared object library, as well as ./lib/libportaudio-x86_64-unknown-linux-gnu.a, a static library. All other things being equal, the linker will prefer to use the shared library (since this is usually what you want) and this is causing your problem.

If you want to link to the shared library, tagging -ldl to the end of your command should fix it (or at least it should fix that problem).

[abhishek2301]

Thanks for your reply!
But there are no files /lib/libportaudio-x86_64-unknown-linux-gnu.so and only *.a file is present in the lib folder. So, there is no chance of linking with a dynamic library.
I also tried with the -static option so that it takes only *.a files but still the same undefined reference errors.
The linking process seems to be very puzzling to me and I could not find any good resource on the web!

Thanks!

[JohnGraham]

But there are no files /lib/libportaudio-x86_64-unknown-linux-gnu.so and only *.a file is present in the lib folder.

Okay - it could be somewhere else on your system. What's the output of doing:

sudo updatedb
locate libportaudio-x86_64-unknown-linux-gnu

In a bash shell?