strange C macro syntax (#var)

What does the # symbol mean when used as a variable prefix in a #define macro?

For example,

#define my_setopt(x,y,z) _my_setopt(x, 0, config, #y, y, z)

From stackoverflow Andrew

• It's the Stringizing Operator, which converts macro parameters to string literals.

  So in your example:

  my_setopt(1, 2, 3)
  

  would expand to:

  _my_setopt(1, 0, config, "2", 2, 3)
  

  From RichieHindle

• # quotes the expression. For example:

  #define SHOW(BAR) printf("%s is %d\n", #BAR , BAR)
  SHOW(3+5);  // prints: 3+5 is 8
  

  From sepp2k