What is the difference between %0.2lf and %.2lf as printf placeholders?

Question

I am aware that putting any number of 0\'s before the width of the placeholder implements zero-padding. For example, printf(\"%02d\", 6); prints

Answer 1

These examples should show the difference:

"%0.2lf", 0.123 -> 0.12 (zero padded min. width of 0, 2 decimal places).

"%6.2lf", 0.123 -> __0.12 (space padded min. width of 6, 2 decimal places).

"%06.2lf", 0.123 -> 000.12 (zero padded min. width of 6, 2 decimal places).

"%0.6lf", 0.123 -> 0.123000 (min width of 0, 6 decimal places).

The first zero specifies zero padding, followed by the minimum width, which has a default of 0. Thus it is effectively ignored by itself (since you cannot pad 0 width).

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Incidentally, the correct form is %f, not %lf for printf.