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#### 14.2.9 Floating-Point Conversions

This section discusses the conversion specifications for floating-point numbers: the ‘`%f`’, ‘`%e`’, ‘`%E`’, ‘`%g`’, and ‘`%G`’ conversions.

The ‘`%f`’ conversion prints its argument in fixed-point notation, producing output of the form [`-`]ddd`.`ddd, where the number of digits following the decimal point is controlled by the precision you specify.

The ‘`%e`’ conversion prints its argument in exponential notation, producing output of the form [`-`]d`.`ddd `e`[`+`|`-`]dd. Again, the number of digits following the decimal point is controlled by the precision. The exponent always contains at least two digits. The ‘`%E`’ conversion is similar but the exponent is marked with the letter ‘`E`’ instead of ‘`e`’.

The ‘`%g`’ and ‘`%G`’ conversions print the argument in the style of ‘`%e`’ or ‘`%E`’ (respectively) if the exponent would be less than -4 or greater than or equal to the precision; otherwise they use the ‘`%f`’ style. Trailing zeros are removed from the fractional portion of the result and a decimal-point character appears only if it is followed by a digit.

The following flags can be used to modify the behavior:

‘`-`’

  Left-justify the result in the field. Normally the result is right-justified.

‘`+`’

  Always include a plus or minus sign in the result.

‘`` ’

  If the result doesn’t start with a plus or minus sign, prefix it with a space instead. Since the ‘`+`’ flag ensures that the result includes a sign, this flag is ignored if you supply both of them.

‘`#`’

  Specifies that the result should always include a decimal point, even if no digits follow it. For the ‘`%g`’ and ‘`%G`’ conversions, this also forces trailing zeros after the decimal point to be left in place where they would otherwise be removed.

‘`0`’

  Pad the field with zeros instead of spaces; the zeros are placed after any sign. This flag is ignored if the ‘`-`’ flag is also specified.

The precision specifies how many digits follow the decimal-point character for the ‘`%f`’, ‘`%e`’, and ‘`%E`’ conversions. For these conversions, the default precision is `6`. If the precision is explicitly `0`, this suppresses the decimal point character entirely. For the ‘`%g`’ and ‘`%G`’ conversions, the precision specifies how many significant digits to print. Significant digits are the first digit before the decimal point, and all the digits after it. If the precision is `0` or not specified for ‘`%g`’ or ‘`%G`’, it is treated like a value of `1`. If the value being printed cannot be expressed precisely in the specified number of digits, the value is rounded to the nearest number that fits.

Next: Other Output Conversions, Previous: Integer Conversions, Up: C-Style I/O Functions [Contents][Index]