dirent.h is a header file that is found only on Linux systems. It provides data structures and function calls to open and read the contents of directories. If you are trying to port Linux code that uses this header file to Windows, you will that it is not available with Visual Studio.
Thankfully, there is a Windows implementation of
dirent.h which can be downloaded here on Github. Just download the zip file, find the
dirent.h header file and place it in your Visual Studio include directory. For example, with Visual Studio Express 2015, this directory is
C:\Program Files (x86)\Microsoft Visual Studio 14.0\VC\include
Tried with: Visual Studio Express 2015 and Windows 7 x64