title: What does the g++ -D flag do?
body: <p>I am looking at a CFLAGS of - </p>
  
  <pre><code>CFLAGS=-g -w -D LINUX -O3 -fpermissive
  </code></pre>
  
  <p>in a Makefile. What does the -D flag do? I see on the man page that </p>
  
  <pre><code>-D name
      Predefine name as a macro, with definition 1. 
  </code></pre>
  
  <p>but I don't know how to interpret that. My interpretation is...its making LINUX a macro and only doing -03 and -fpermissive when in a linux environment. Is that right? If not, then what? Thanks for any help</p>