On 1ÔÂ8ÈÕ, ÉÏÎç7ʱ23·Ö, rochus wrote:
> Hi!
>
> I have some problems getting around with shared libraries under linux.
> I'm an experienced Delphi developer and way used to the windows way of
> DLLs, so don't blame me as I may still think too much in the way of how
> things are down in Windows/Delphi...
>
> Allright, here we go: At the moment I try to learn how to write shared
> objects under linux and have some problems. I read the HOWTO on
> [1]tldp.org and I read [2]IBM's paper on the topic, but both didn't
> really work. Now here is what i've done so far that still won't work.
> I'm a bit frustrated now, as it seems that libraries under linux are way
> harder to write/use/bla than it was under windows:
>
> 1. I created the file "libhello.c":
> #include "stdio.h"
>
> void hello(void) {
> printf("Hello, this comes from within a library");
> }
>
> 2. I created the header file "libhello.h":
> void hello(void);
>
> 3. I created a "client"-app (demo_use.c):
> #include "libhello.h"
>
> int main(void) {
> hello();
> return 0;
> }
>
> 4. I compiled and linked the library:
> gcc -fPIC -c libhello.c
> ld -shared -soname libhello.so.1 -o libhello.so.1.0 -lc libhello.o
>
> 5. I copied the .so* files to /usr/local/lib
>
> 6. I ran "ldconfig -v -n ." when located in /usr/local/lib
>
> 7. I created an additional symbolic link to the libhelloso.1.0 fiel:
> ln -s libhello.so.1.0 libhello.so
>
> 8. I compiled the demo client:
> gcc -o demo_use demo_use.c -lhello
>
> 9. I tried to run "demo_use", but everything I get is:
> "error while loading shared libraries: libhello.so.1: cannot open
> shared object file: No such file or directory"
>
in /usr/lib/:

ln -s libhello.so.1.0 libhello.so.1

> Now im stuck with this and don't really know what to do. It would be
> really nice if you could tell me how to install the library properly
> and/or show me a howto where the "shared object"-topic is covered a bit
> better than in those I just read...
>
> Best Regards and sorry for my english, it seems to be rusty
> Nicolai Waniek
>
> [1]http://www.tldp.org/HOWTO/Program-Library-HOWTO/index.html
> [2]http://www-128.ibm.com/developerworks/library/l-shobj/

rochus writes:

> I'm a bit frustrated now, as it seems that libraries under linux are way
> harder to write/use/bla than it was under windows:

Actually they are simpler to write: all you need is:

gcc -fPIC -shared -o libhello.so hello.c &&
cp libhello.so /usr/local/lib

> 4. I compiled and linked the library:
> gcc -fPIC -c libhello.c
> ld -shared -soname libhello.so.1 -o libhello.so.1.0 -lc libhello.o

Never use 'ld' directly, unless you *know* what you are doing. Always
use correct compiler driver (gcc for C, g++ for C++) instead.

> 7. I created an additional symbolic link to the libhelloso.1.0 fiel:
> ln -s libhello.so.1.0 libhello.so

The problem is that you are trying to learn too many things at once:
- how to create shared libraries,
- how to use external versioning (the -soname and the symlink
business).

> It would be
> really nice if you could tell me how to install the library properly

In /usr/local/lib you need:

# Actual library
libhello.so.1.0

# Symlink that could later point to an updated version, e.g.
# libhello.so.1.0.3, or libhello.so.1.1
# This symlink is used by the runtime linker, because "libhello.so.1"
# is encoded into the executable as a dependency.

libhello.so.1 -> libhello.so.1.0

# Finally, you need a symlink for (static) linker:

libhello.so -> libhello.so.1

> and/or show me a howto where the "shared object"-topic is covered a bit
> better than in those I just read...

I find Sun "Linker and Libraries Guide" clearer than Linux docs:
http://docs.sun.com/app/docs/doc/817-1984

Cheers,
--
In order to understand recursion you must first understand recursion.
Remove /-nsp/ for email.

"Bin Chen" writes:

>> 5. I copied the .so* files to /usr/local/lib
>>
> in /usr/lib/:
> ln -s libhello.so.1.0 libhello.so.1

That wouldn't work, since his libs are *not* in /usr/lib.

Cheers,
--
In order to understand recursion you must first understand recursion.
Remove /-nsp/ for email.

Thanks alot Paul!
Both for your advise and the link to the sun documentation. First it
didn't seem to work your way until I found out that /usr/local/lib was
missing on the ld.so search path.

best regards,
Nicolai Waniek