Unfamiilar macro expansion

Question

I am familiar with std #defines and macro expansion for min max function but this one throws me. In particular the #'s in the definition. Your thoughts appreciated.

#define TAB_WIDGET_ROW(t)     {t##_seq, t##_len, t##_rep}

Answer 1

You should read some documentation concerning the C Preprocessor. The ## is about Concatenation. So an invocation like TAB_WIDGET_ROW(xy) of your TAB_WIDGET_ROW macro would probably be expanded to {xy_seq, xy_len, xy_rep}

Answer 2

The ## is a C preprocessor standard macro used for concatenation.

This way, the code :

#define TAB_WIDGET_ROW(t)     {t##_seq, t##_len, t##_rep}

int foo[3] = TAB_WIDGET_ROW(bar);

Will expand to :

int foo[3] = {bar_seq, bar_len, bar_rep};

And the foo array will be filled with values of variables bar_seq, bar_len and bar_rep.

See here for more informations.