Why is the 'max' macro defined like this in C?

Question

 #define max(a,b) \\
   ({ typeof (a) _a = (a); \\
       typeof (b) _b = (b); \\
     _a > _b ? _a : _b; })

Why not simply (a>b ? a :

Answer 1

Another way to determine max (at least for positive numbers)

#define MAX(a,b) sizeof(union x { char ca[a]; char cb[b];})

As a and b are accessed only once, MAX(a++,b++) gives the correct result.