[gandalf013]

A very common idiom is "T p = malloc(n sizeof *p)". That only works if sizeof doesn't evaluate its arguments.

[kazinator]

Why not? Suppose you have a C99 VLA object, and you want to malloc the equivalent amount of space. Couldn't you just do this:

   int vla[nparam];
   int *pcopyspace = malloc(sizeof vla);

Here sizeof vla is basically just nparam sizeof(int).

vla* is evaluated to the extent of calculating its run-time size.