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 06.
But what does putting a single 0 before the precision of the placeholder do? For example, for both printf("%0.2lf", 0.123); and printf("%.2lf", 0.123);, the output is 0.12.
If it does nothing, is there a preferred format?
They are "equivalent". If you were to use "%07.2", then it would make a difference, by adding extra zeros on the front.
Edit: Originally had "%04.2", which of course doesn't make any difference, because a float with two decimals is always 4 wide anyway.
%3.2f //(print as a floating point at least 3 wide and a precision of 2)
%0.2lf //(print as a floating point at least 0 wide and a precision of 2)
%.2lf //(print as a floating point at least 0(default) wide and a precision of 2)
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).
%f, not %lf for printf.
Blockquote
Basically when we % w.p f for output w refers to the minimum number of position to be use for displaying the value and p refers to the number of digit after decimal point.
%3.2f floating point having 3 wide and 2 number after decimal
%0.2ffloating point at least 0 wide and 2 number after decimal
%.2f floating point at least 0(default) wide and a precision of 2)
But don't misunderstand about the 0 width if you use %0.2f it can auto adjust its minimum width.
