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<title>User created libraries/archives</title>
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<h1>User created libraries/archives</h1>
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<p>
Wot is a user library? I hear you ask! Well, its a collection of your
functions, that, when placed into a library are available to all the programs
you write.<p>
This is what
<a href="../CONTRIB/SAWTELL/c-lesson.7">Chris Sawtell</a>
has to say about libraries.
<p>
There are two types of library, <a href="dynamic.htm">dynamic</a>
and static. Although dynamic libraries
are the prefered alternative (because they are not linked
into your program), here is the method required to create
static libraries....
<p>
There are several steps required in creating a library.<p>
<ul>
<li>Create a function.
<li>Create an object module of the function.
<li>Add the object module to the library/archive.
<li>Compile a program that uses the library/archive.
</ul>
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Here are the four steps in UNIX terms. The function is called <b>reverse</b>
and the library is called <b>mart</b>.
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vi reverse.c # write your function (no main).
gcc -c reverse.c # -c just compiles (no link).
ar -q libmart.a reverse.o # -r == if nessasary replace
# an existing function.
gcc program.c -lmart -L/home/leslim # -l == library to search
# -L == Location of the library.
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<p>
A few notes:<p>
<ul>
<li>reverse.c should NOT contain a <b>main</b>.
<li>A header file containing the prototype for reverse.c is required.
<li>I expected to be able to add /home/leslim to LD_LIBRARY_PATH but
gcc does not seem to look at this variable for its list of libraries.
<li>If you dont want to use the <b>-L</B> option you will have to place
your library in a directory like <b>/usr/lib</b>.
<li>DONT LOOSE THE SOURCE! You cant rebuild the source from the object
module. If you want to make a change at a later date you will want
the source.
</ul>
<hr>
Other usefull commands:
<ul>
<li>ar -t libmart.a == List the Objects in a library.
</ul>
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<h2>See Also:</h2>
<ul>
<li><a href="syscalls.htm">System calls and Library calls.</a>
</ul>
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<address>Martin Leslie
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