Re: .so and .a libraries

[Paul Pluzhnikov]

Robert Heller <heller@deepsoft.com> writes:

>   "Morusaka" <morusaka@inwind.it>,

> "> g++ -IpathDirectory -LlibraryDirectory -llibraryName sourcefilename.cpp

This command-line is "backwards"; libraries should always *follow*
objects and sources, never preceed them:

  g++ -IpathDirectory source.cpp -L... -l...

> You have two options:

Five options:

> 1) Embed the libraryDirectory in your executable:
> 
> g++ -IpathDirectory -LlibraryDirectory -Lrpath=libraryDirectory -llibraryName 
> sourcefilename.cpp

Correction: make that

  g++ -IpathDirectory source.cpp -Wl,-rpath=libraryDirectory -L... -l...

> 2) Use the LD_LIBRARY_PATH environment variable:

3) Add libraryDirectory to the /etc/ld.so.conf and run /sbin/ldconfig.

4) Link against the archive version of the library:

  g++ -I... source.cpp /path/to/library.a
or
  g++ -I... source.cpp -L/path/to -Wl,-Bstatic -llibraryName -Wl,-Bdynamic

> "> How can I link to my executable the ".a" library files?

See the 2 commands above.

> g++ -static -IpathDirectory -LlibraryDirectory -llibraryName 
> sourcefilename.cpp

The above -- linking completely static executable -- is extremely bad idea(TM).

> I think.  I am not sure if you really want to do this -- you will likely
> get a *huge* executable, since it is likely to link ALL of the system
> libraries statically. 

Not only that, but your executable will likely break if/when you
move it to machines with newer versions of glibc [dynamically-linked
executables generally continue to work fine under these conditions].

5)
> Oh, you *could* also copy the .so file to /usr/local/lib and make sure
> /usr/local/lib is in /etc/ld.so.conf and re-run /sbin/ldconfig (as
> root).  This will make the .so file visible to the run-time loader,
> automagically. 

Cheers,
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