Question

I have seen this macro defined before but never really knew its purpose. Can anyone shed light on this?

Answer 1

This is a compiler intrinsic used for optimization, typically seen in embedded programming. The only time I have seen it used is in the ‘default’ for a switch statement to assert that the variable has a limited range (for better optimization). Example:

 /* Get DTMF index */  switch(dtmf)  {      case '0':      case '1':      case '2':      case '3':      case '4':      case '5':      case '6':      case '7':      case '8':      case '9':          /* Handle numeric DTMF */          index = dtmf - '0';          break;      case 'A':      case 'B':      case 'C':      case 'D':          index = dtmf - 'A' + 10;          break:      default:          _never_executed();          break;  } 

Probably doesn’t work with all compilers…