Insert error "HELLO" "and" WORLD "" does not give a valid preprocessing token

Question

This is a bad code.

#include<stdio.h> #define CAT_I(A, B) A ## B #define CAT(A, B) CAT_I(A,B) void main (void) { printf(CAT("HELLO","WORLD")); } 

Why does this give this error? How can i fix this?

EDIT

This is what I'm trying to do.

 #define TAG "TAG" #define PRE CAT(CAT("<",TAG),">") #define POS CAT(CAT("</",TAG),">") #define XML CAT(CAT(PRE,"XML SOMETHING"),POS) 

then

 printf(XML); 

Answer 1

Result ## must be one token, and "HELLO""WORLD" - not one token. To concatenate the lines, just leave them next to each other:

 printf("HELLO" "WORLD"); 

Or change your macro to remove ## .

 #define CAT(A, B) AB 

String literals are combined together when there are no intermediate tokens between them.