Question

something like #NAME or ##NAME. what do they mean in C? I saw them in GCC documents about macro.

Answer 1

operator ## concatenates two arguments leaving no blank spaces between them..

 #define printe(a,b) a ## b
   printe(c,out) << "testing";

output is : testing

and single # is used for parameter replacement withe the string parameter
like

#define  st(x)  #x
 cout<<st(tesing); //  equivalent to  cout<<"testing";

and # is also a preprocessor directive..