title: What is a "packed" structure in C?
body: <p>I am going though some C code written for the Microchip C30 compiler and I often see structs defined as follows:</p>
  
  <pre><code>typedef struct __attribute__((__packed__)) 
  {
      IP_ADDR     MyIPAddr;               // IP address
      IP_ADDR     MyMask;                 // Subnet mask
      IP_ADDR     MyGateway;              // Default Gateway
          // etc...
  } APP_CONFIG;
  </code></pre>
  
  <p>What does packed mean?</p>