 |
C++Talk.NET
C++ language newsgroups
|
| View previous topic :: View next topic |
| Author |
Message |
happyvalley
Guest
|
 Posted: Tue Jun 13, 2006 9:10 am Post subject: why link against a library? |
 |
|
a silly question.
when linking a program,
the path to include files and library files are given already (-I, -L),
why still need to give the names of some library by -l , say -lm for
math library. otherwise, will get no reference error
thanks |
|
| Back to top |
|
 |
Dirk Feytons
Guest
|
| Posted: Tue Jun 13, 2006 9:10 am Post subject: Re: why link against a library? |
|
|
happyvalley wrote:
| Quote: | a silly question.
when linking a program,
the path to include files and library files are given already (-I, -L),
why still need to give the names of some library by -l , say -lm for
math library. otherwise, will get no reference error
|
-I and -L specify directories where respectively header files and
libraries can be found. They are different things so they don't
necessarily live in the same place. On a typical Linux system for
instance header files can be found in /usr/include while libraries are
in /lib.
The -l switch tells the linker which specific libraries to link against.
Just like you used #include to tell which header files to use for
compilation of a translation unit.
Header files typically only hold declarations. It just tells what
certain structures look like and which functions exist somewhere so the
compiler knows how to compile a translation unit. After that you still
need the actual code of those functions to create a working program.
See also
http://groups.google.com/group/comp.lang.c++/browse_frm/thread/3274db962f1f060c/8e616babfa4cbc97?lnk=st&q=linking+author%3Akarl+author%3Aheinz&rnum=1&hl=en#8e616babfa4cbc97
--
Dirk
(PGP keyID: 0x448BC5DD - http://www.gnupg.org - http://www.pgp.com) |
|
| Back to top |
|
|
Jack Klein
Guest
|
| Posted: Tue Jun 13, 2006 9:10 am Post subject: Re: why link against a library? |
|
|
On 12 Jun 2006 21:57:56 -0700, "happyvalley"
<nittanymountain (AT) gmail (DOT) com> wrote in comp.lang.c++:
| Quote: | a silly question.
when linking a program,
the path to include files and library files are given already (-I, -L),
why still need to give the names of some library by -l , say -lm for
math library. otherwise, will get no reference error
thanks
|
Note that linkers and their operation are not really topical here,
since they are not defined by the language, and differ from one
compilers to another.
But in general, the path or set of paths that you specify to the
linker to search for libraries might contain dozens or hundreds of
them. A linker could be designed to search every single one of them
to see if it contains anything it needs, but there are two problems
with that approach.
The first is that it could make building an executable take much
longer.
The second is that a symbol could be defined in more than one library,
leading either to multiple definitions, or an executable that builds
without error but uses the wrong function or object.
--
Jack Klein
Home: http://JK-Technology.Com
FAQs for
comp.lang.c http://c-faq.com/
comp.lang.c++ http://www.parashift.com/c++-faq-lite/
alt.comp.lang.learn.c-c++
http://www.contrib.andrew.cmu.edu/~ajo/docs/FAQ-acllc.html |
|
| Back to top |
|
|
Marco Wahl
Guest
|
| Posted: Tue Jun 13, 2006 9:10 am Post subject: Re: why link against a library? |
|
|
a silly question.
| Quote: |
when linking a program,
the path to include files and library files are given already (-I, -L),
why still need to give the names of some library by -l , say -lm for
math library. otherwise, will get no reference error
|
This is merely a platform question than a C++ question.
In typical compile-link tools '-I' is used to specify
an include path, '-L' the path where to find libraries
and '-l' the name of the library. So all three are useful.
HTH |
|
| Back to top |
|
|
|
|
You cannot post new topics in this forum
You cannot reply to topics in this forum
You cannot edit your posts in this forum
You cannot delete your posts in this forum
You cannot vote in polls in this forum
|
|
FAQ
Search
Memberlist
Usergroups
Register
Profile
Log in to check your private messages
Log in
