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    <p>Dynamic linking on Mac OS X, a tiny example</p> <p>Steps: </p> <ol> <li>create a library libmylib.dylib containing mymod.o </li> <li>compile and link a "callmymod" which calls it </li> <li>call mymod from callmymod, using DYLD_LIBRARY_PATH and DYLD_PRINT_LIBRARIES</li> </ol> <p>Problem: you "just" want to create a library for other modules to use. However there's a daunting pile of programs -- gcc, ld, macosx libtool, dyld -- with zillions of options, some well-rotted compost, and differences between MacOSX and Linux. There are tons of man pages (I count 7679 + 1358 + 228 + 226 lines in 10.4.11 ppc) but not much in the way of examples, or programs with a "tell me what you're doing" mode.</p> <p>(The most important thing in understanding is to make a simplified OVERVIEW for yourself: draw some pictures, run some small examples, explain it to someone else).</p> <p>Background: <a href="https://developer.apple.com/library/mac/documentation/DeveloperTools/Conceptual/DynamicLibraries/100-Articles/OverviewOfDynamicLibraries.html" rel="nofollow noreferrer">apple OverviewOfDynamicLibraries</a>, <a href="http://en.wikipedia.org/wiki/Dynamic_library" rel="nofollow noreferrer">Wikipedia Dynamic_library</a></p> <hr> <p>Step 1, create libmylib.dylib --</p> <pre><code>mymod.c: #include &lt;stdio.h&gt; void mymod( int x ) { printf( "mymod: %d\n", x ); } gcc -c mymod.c # -&gt; mymod.o gcc -dynamiclib -current_version 1.0 mymod.o -o libmylib.dylib # calls libtool with many options -- see man libtool # -compatibility_version is used by dyld, see also cmpdylib file libmylib.dylib # Mach-O dynamically linked shared library ppc otool -L libmylib.dylib # versions, refs /usr/lib/libgcc_s.1.dylib </code></pre> <hr> <p>Step 2, compile and link callmymod --</p> <pre><code>callmymod.c: extern void mymod( int x ); int main( int argc, char** argv ) { mymod( 42 ); } gcc -c callmymod.c gcc -v callmymod.o ./libmylib.dylib -o callmymod # == gcc callmymod.o -dynamic -L. -lmylib otool -L callmymod # refs libmylib.dylib nm -gpv callmymod # U undef _mymod: just a reference, not mymod itself </code></pre> <hr> <p>Step 3, run callmymod linking to libmylib.dylib --</p> <pre><code>export DYLD_PRINT_LIBRARIES=1 # see what dyld does, for ALL programs ./callmymod dyld: loaded: libmylib.dylib ... mymod: 42 mv libmylib.dylib /tmp export DYLD_LIBRARY_PATH=/tmp # dir:dir:... ./callmymod dyld: loaded: /tmp/libmylib.dylib ... mymod: 42 unset DYLD_PRINT_LIBRARIES unset DYLD_LIBRARY_PATH </code></pre> <p>That ends one tiny example; hope it helps understand the steps.<br> (If you do this a lot, see <a href="http://en.wikipedia.org/wiki/Libtool" rel="nofollow noreferrer">GNU Libtool</a> which is glibtool on macs, and <a href="http://www.scons.org" rel="nofollow noreferrer">SCons</a>.)<br> cheers<br> -- denis</p>
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    1. POHow do I create a dynamic library (dylib) with Xcode?
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    1. COnice. what if you already have the .o files, but there are say, 9 of them, in the 3 folders, but all part of the same "framework"... is this a call to arms for lipo, or what? btw i'm trying to get libg7221 to "be" a "shared" "library", in this case...
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    2. CO@alex gray, don't know, sorry; ask that as a new question ?
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