Question

I have a macro defined in C something like this:

  #define SOME_FIELD(_A_,_B_,_C_) \
    MyObj[ ## _A_ ## ].somePTR =        \
    (DWORD_PTR) (buff_ ## _C_  ## _C_ ## _ ## _B_ ## );

What i can understand that for index A we are getting some value for “somePTR”. My question is, What is ## <name> ## notation for and with this how value of somePTR is calculated??

I am new to such a macro so a descriptive explanation would be very helpful.

Answer 1

That is called token concatenation. It allows you to glue arguments together.

For your example, SOME_FIELD(Param1,Param2,Param3); expands like this:

MyObj[Param1].somePTR = (DWORD_PTR) (buff_Param3Param3_Param2);

It’s easy enough to try this out yourself by using your compiler’s pre-processor. You don’t generally need to go to the trouble of writing a fully-fledged C program—the pre-processor can generally be invoked by itself.