title: What is `S_ISREG()`, and what does it do?
body: <p>I came across the macro <code>S_ISREG()</code> in a C program that retrieves file attributes. Unfortunately, there isn't any basic information about this macro online. There are some more advanced discussions on it, but they go beyond what I'm looking for. </p>
  
  <p>What is <code>S_ISREG()</code>, and what does it do? In the context of a program that retrieves file attributes, what purpose does it serve, and exactly what does it do?</p>
  
  <p>Thank you.</p>