Modular programming

As the size of applications increases, the job of developers is to try to divide it into several modules. Each module aims to be independent and reusable, and each is maintained by different developer teams. The main application simply initializes, imports, and uses these modules. This makes the process of building a larger application more efficient.

The following example shows the dependencies for nginx (https://www.nginx.com) on CentOS 7. It indicates that nginx uses OpenSSL(libcrypt.so.1, libssl.so.10), the POSIX thread(libpthread.so.0) library, the regular expression PCRE(libpcre.so.1) library, the zlib(libz.so.1) compression library, the GNU C(libc.so.6) library, and so on:

$ /usr/bin/ldd /usr/sbin/nginx
  linux-vdso.so.1 =>  (0x00007ffd96d79000)
  libdl.so.2 => /lib64/libdl.so.2 (0x00007fd96d61c000)
  libpthread.so.0 => /lib64/libpthread.so.0   
  (0x00007fd96d400000)
  libcrypt.so.1 => /lib64/libcrypt.so.1   
  (0x00007fd96d1c8000)
  libpcre.so.1 => /lib64/libpcre.so.1 (0x00007fd96cf67000)
  libssl.so.10 => /lib64/libssl.so.10 (0x00007fd96ccf9000)
  libcrypto.so.10 => /lib64/libcrypto.so.10   
  (0x00007fd96c90e000)
  libz.so.1 => /lib64/libz.so.1 (0x00007fd96c6f8000)
  libprofiler.so.0 => /lib64/libprofiler.so.0 
  (0x00007fd96c4e4000)
   libc.so.6 => /lib64/libc.so.6 (0x00007fd96c122000)
   ...