Extra leading zeros when printing float using printf?

I'd like to be able to write a time string that looks like this: 1:04:02.1 hours using printf.
When I try to write something like this:

printf("%d:%02d:%02.1f hours\n", 1, 4, 2.123456);

I get:

1:04:2.1 hours

Is it possible to add leading zeros to a float formatting?

With the %f format specifier, the "2" is treated as the minimum number of characters altogether, not the number of digits before the decimal dot. Thus you have to replace it with 4 to get two leading digits + the decimal point + one decimal digit.

printf("%d:%02d:%04.1f hours\n", 1, 4, 2.123456);

Try %04.1f instead of %02.1f. The "4" here means at least 4 characters will be printed, and "2.1" has 3 (> 2) characters, so to enable the padding zeros you need 4.