Creating C Dynamic Libraries in Linux

  Dynamic library is a relocatable object file with metadata. Dynamic libraries are linked at run time. They are built from one or more object files ( .o files). In Linux Dynamic libraries are called shared objects and the extension is .so. The name of a Dynamic library should start with lib. For example libtest.so is a valid Dynamic library name. 

Creating the Dynamic Library File

Let the name of the C Program file be p1.c,

• Creating object files: Use gcc to create object files as Position independent Code as follows.

          gcc -fPIC -c p1.c 

• Creating the Shared Object: 

          gcc -shared p1.o -o libtest.so

Storing & Linking the Static Library File

You need to change the LD_LIBRARY_PATH as follows,

 export LD_LIBRARY_PATH=$LD_LIBRARY_PATH:/newpath

• Store the dynamic library in the standard directory /usr/lib. 

          Compile & link the dynamic library file with target.c as follows,
          gcc target.c -ltest

• Store the static library in a directory you have created. 

          For example in /usr/student/mylib.
          Compile & link the static library file with target.c as follows,
          gcc target.c -L/usr/student/mylib -ltest

• You can also change the LD_LIBRARY_PATH as follows so that the compiler will search even the new path, 

          export LD_LIBRARY_PATH=$LD_LIBRARY_PATH:/usr/student/mylib

          Now compile & link the dynamic library file with target.c as follows,
          gcc target.c -ltest