Comment author: @gasche

Note that both "%10s" "%.10s" pad when the input string is less than 10 characters (and you can use "-" for padding to the right, but 0-padding is ignored). The part that was never implemented is cutting the input when the width specification is smaller than the string size.

Comment author: acascella

The part that was never implemented is cutting the input when the width specification is smaller than the string size.

Actually specifying a width smaller than the size of the string has no effect:

printf("%2s", "Hello") will print "Hello".

The width gives the minimum width of the field.
The precision the maximum number of bytes to write.

The format '%x.ys' will print at most y chars into a field of size x, padding with spaces if needed.

On the other side, if a precision is given, the cutting takes place whatever the width specified, before eventually padding to the minimum width.

printf("%10.2s", "Hello") will print "________He". (where _ = space).

So it would be useful to have both width and precision in string formats.

Comment author: bvaugon

This feature may be easy to implement, I think, and sometimes useful.
Another useful feature may be to print ellipsis when the string is
truncated.

However, remarks that truncating a string "anywhere" is "dangerous"
when you print (for example) some utf8 data because you may truncate a
multi-byte character.

Comment author: @gasche

One think I like with this proposal is that at least it gives a clear specification of what the padding and precision numbers do for non-floating-point parameters.

Comment author: acascella

@bvaugon: you're right, truncation should be done by number of chars and not bytes, in order to avoid that kind of problem with multi-byte characters.

@gasche: I think it is a good idea to use the C specification, which is clear and precise, when possible. (You can have a look at http://www.open-std.org/jtc1/sc22/wg14/www/docs/n1256.pdf starting page 274 for the printf family functions).

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