c - Reading Zend Engine API code: What does ## (double hash) mean?

Question

Out of curiousity, I'm reading the Zend Engine API code and encountered quite a number of ## in their #define's. For example, at /usr/lib/php5/Zend/zend_API.h:

#define ZEND_FN(name) zif_##name
#define ZEND_MN(name) zim_##name

What does the ## (double hash) symbols mean in these two lines?

Answer 1

The ## concatenates what's before the ## with what's after it. So in your example doing ZEND_FN(foo) would result in zif_foo