POSIX specifies a dprintf function that operates on an fd instead of
a stdio stream. Using upper case for macros is more idiomatic too.
We no longer need to use an extra set of parentheses for debugging
- sprinkle const
- add a macro (setptr) that cheats const to temporarily NUL terminate strings
remove casts from allocations
- use strdup instead of strlen+strcpy
- use x = malloc(sizeof(*x)) instead of x = malloc(sizeof(type of *x)))
- add -Wcast-qual (and casts through unitptr_t in the two macros we
cheat (xfree, setptr)).