Why Does `fmt.Printf` with `%g` and Width/Precision Fields Behave Unexpectedly?

fmt.Printf with Width and Precision Fields in %g Behaves Unexpectedly

When trying to format floats with a consistent width using fmt.Printf(), it may not behave as expected when using the %g format specifier with both width and precision fields.

According to the documentation, the precision field for %g sets the number of total digits, excluding any leading zeros. However, the %g format specifier has some unique behaviors that can be confusing.

Leading Zeros and Digit Counting:

• Leading zeros in the fractional part are not counted as digits.
• Trailing zeros after non-zero digits are counted as digits.

Examples:

• fmt.Printf("%.4g", 0.12345) gives 0.1235.
• fmt.Printf("%.4g", 0.012345) gives 0.01235.
• fmt.Printf("%.4g", 0.0012345) gives 0.001234.

Precision and Width:

• The width field specifies the minimum width, including any decimal points or exponents.
• If the number of digits exceeds the specified width, the width field will be ignored.

Your Case:

In your example, you used .9g, which specifies a minimum width of 10 and a total of 9 digits. However, the following behaviors occur:

• 0.0606060606060606: Requires 12 digits, so the minimum width is ignored.
• 0.3333333333333333: Requires 11 digits, so the minimum width is ignored.
• 0.05 and 0.4: Require 9 digits, which are less than the minimum width, so they are padded with spaces.
• 0.1818181818181818: Requires 9 digits after rounding, so the minimum width is ignored.

The above is the detailed content of Why Does `fmt.Printf` with `%g` and Width/Precision Fields Behave Unexpectedly?. For more information, please follow other related articles on the PHP Chinese website!