C Library Creation

How to generate a library:

* Compile: cc -c ctest1.c ctest2.c
* Create library "ctest.a": ar -cvq ctest.a ctest1.o ctest2.o
* List files in library: ar -t ctest.a
* Using library: cc -o executable-name prog.c ctest.a
* Example files:
      o ctest1.c

        ctest1(int *i)
        {
         *i=5;
        }

      o ctest1.c

        ctest1(int *i)
        {
         *i=100;
        }

      o prog.c

        #include <stdio.h>
        main()
        {
           int x;
           ctest1(&x);
           printf("Valx=%d\n",x);
        }

Historical note: After creating the library it was once necessary to run the command: ranlib ctest.a. This created a symbol table within the archive. Ranlib is now embedded into the “ar” command.

How to generate a shared object: (Dynamically linked object library file.)

    gcc -fPIC -c *.c
    gcc -shared -Wl,-soname,libfoo.so.1 -o libfoo.so.1.0   *.o

Notes: * Option -fPIC: Compiler directive to output position independent code suitable for dynamic linking. * Pass options to linker as -Wl. In example above options to be passed on to linker are: “-soname libfoo.so.1”. * Option -shared: Produce a shared object which can then be linked with other objects to form an executable. * Option -o: Output of operation. In this case the name of the shared object to be output will be “libfoo.so.1.0

Man Pages: * gcc - GNU C compiler * ld - The GNU Linker

Multiple Static Declarations: Multiple Static declarations.

[root@xe30-1][~/rkks/test/lib]$ gcc -o prog prog.c test.a prog.c:3: error: multiple storage classes in declaration of a' [root@xe30-1][~/rkks/test/lib]$ gcc -o prog prog.c -L. -ltest prog.c:3: error: multiple storage classes in declaration ofa’

Useful Libraries

general : libglib / libgobject / libpthread/libevent console : libncurses 2D graphics : libX11 / libSDL 3D graphics : libGL / libGLU / libGLUT GUI toolkits : libgtk / libQT Images : libjpeg / libpng / libgif text rendering : libpango / libfreetype sound : libasound / libSDL compression : libz (zlib) / libgzip / libbz2 encryption : libcrypt / libssl / libgssapi / libkrb5 XML : libxml2, Xerces XML parser web : libcurl debug: libbfd, libiberty, libopcodes Documentation: doxygen C Frameworks - apr PHP Frameworks - CodeIgnitor, Yii, Zend, Symfony Java Frameworks - ant, cmake config file parser: libconfuse

apptrace diffstat -xprofile -

Local/Non-root installation advisory

If you ever happen to want to link against installed libraries in a local directory, LIBDIR, you must either use libtool, and specify the full pathname of the library, or use the -LLIBDIR' flag during linking and do at least one of the following: - add LIBDIR to theLD_LIBRARY_PATH’ environment variable during execution - add LIBDIR to the LD_RUN_PATH' environment variable during linking - use the-Wl,-rpath -Wl,LIBDIR’ linker flag - have your system administrator add LIBDIR to `/etc/ld.so.conf’