Padding a multiline C macro in vim - vim

Question

I have C macros like:
#define MY_MACRO() \
xxxxx xxxxxxx \
xxxxxx xxxxxxx \
xx xxxxxxxxxx xxxxxx x xxxxxxx xxxxxxxx \
xxxxx \
xxxxxx xxxxxxx \
xxxxxx x xxxxxxxxx xx xxxxxxxxx x \
xxxxxxxxxx xxxxxxxxxxxxxx \
x xxxxxxxxxxxxx xxxxxxxxxxxxxxxxxxx \
xxxxxx x xxxxxx x xxxxxxxx x xxxxxx x xxxxxxxxx \
x \
xxx x xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx \
xxxxxxxxxxxxxxxxxxxxxxxxx xxx \
xxxxx \
xxxxxx xxxxxxxxxxxxxxxx xxxxxxxxxxxxxxxx x \
x xx xx xxxxxxx
And I'm trying to pad them to:
#define MY_MACRO() \
xxxxx xxxxxxx \
xxxxxx xxxxxxx \
xx xxxxxxxxxx xxxxxx x xxxxxxx xxxxxxxx \
xxxxx \
xxxxxx xxxxxxx \
xxxxxx x xxxxxxxxx xx xxxxxxxxx x \
xxxxxxxxxx xxxxxxxxxxxxxx \
x xxxxxxxxxxxxx xxxxxxxxxxxxxxxxxxx \
xxxxxx x xxxxxx x xxxxxxxx x xxxxxx x xxxxxxxxx \
x \
xxx x xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx \
xxxxxxxxxxxxxxxxxxxxxxxxx xxx \
xxxxx \
xxxxxx xxxxxxxxxxxxxxxx xxxxxxxxxxxxxxxx x \
x xx xx xxxxxxx
The lines should be 80 chars total.
'<,'>s/\(.*[^\s]\)\s*\\\s*$/\=printf('%-79s\', submatch(1))
mostly does it, except for lines such as:
xxxxxx xxxxxxx \
that exceed the 80 char limit to star with.
What am I doing wrong?

Answer 1

The printf() width specifier only adds padding to increase the string. If it is already larger than the width, it does not cut off anything.
Your regular expression attempts to limit the matching by excluding trailing whitespace from the match group. Unfortunately, this does not work: [^\s]. You cannot use atoms like \w inside a collection. Either use the corresponding character class ([^[:white:]]), or, if available, the negated atom: \S. With this fix, your substitution works just fine:
'<,'>s/\(.*\S\)\s*\\\s*$/\=printf('%-79s\', submatch(1))