How does fmt.Printf\'s %g format handle width and precision fields when dealing with leading zeroes?

Behavior of fmt.Printf with Width and Precision Fields for %g

In fmt.Printf, the %g format for floating-point values offers flexibility in specifying both width and precision. However, there are nuances to consider when using these fields in combination.

Precision and Total Digits

Unlike other floating-point formats (%f and %e), for %g, the precision field specifies the total number of digits after the decimal place (excluding leading zeroes and exponent). For example, %.4g ensures a total of four digits, regardless of any leading zeroes.

Leading Zeroes and Minimum Width

Leading zeroes are counted as digits for precision but are excluded in calculating the minimum width. The minimum width determines the overall field width and is set using the width field (e.g., g).

How .9g Behaves

In your specific case, .9g specifies a total of nine digits (excluding leading zeroes) and a minimum width of 10 characters:

• For 0.0606060606060606, nine digits without leading zeroes give 0.0606060606, which already meets the minimum width of 10.
• For 0.3333333333333333, nine digits without leading zeroes give 0.333333333, also satisfying the minimum width.
• For 0.05, nine digits without leading zeroes give 0.05, which falls short of the minimum width of 10, so it is padded to fill the remaining six characters.
• The same applies to 0.4.
• For 0.1818181818181818, nine digits without leading zeroes give 0.181818182 (with rounding), which again meets the minimum width.

So, in summary, the different outputs for your input values are due to the interaction between precision (determining the number of displayed digits) and minimum width (ensuring a certain field width).

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