Token Pasting (##)

The token-pasting operator (##) within a macro definition combines two arguments. It permits two separate tokens in the macro definition to be joined into a single token.

If the name of a macro parameter used in the macro definition is immediately preceded or followed by the token-pasting operator, the macro parameter and the token-pasting operator are replaced by the value of the passed parameter. Text that is adjacent to the token-pasting operator that is not the name of a macro parameter is not affected. For example:

#define tokenpaster(n) printf ("token" #n " = %d", token##n)

tokenpaster(34);

This example results in the following actual output from the preprocessor:

printf ("token34 = %d", token34);

This example shows the concatenation of token##n into token34. Both the stringize and the token-pasting operators are used in this example.