The format has to follow the C-conventions.

The following escape sequences produce the associated action on display devices capable of the action:

\a

Alert. Ring the bell.

\b

Backspace. Move the printing position to one character before the current position, unless the current position is the start of a line.

\f

Form feed. Move the printing position to the initial printing position of the next logical page.

\n

Newline. Move the printing position to the start of the next line.

\r

Carriage return. Move the printing position to the start of the current line.

\t

Horizontal tab. Move the printing position to the next implementation-defined horizontal tab position on the current line.

\v

Vertical tab. Move the printing position to the start of the next implementation-defined vertical tab position.

Each conversion specification is introduced by the character %. After the character %, the following appear in sequence:

An optional field, consisting of a decimal digit string followed by a $, specifying the next args to be converted. If this field is not provided, the args following the last args converted will be used.

Zero or more flags, which modify the meaning of the conversion specification.

An optional string of decimal digits to specify a minimum field width. If the converted value has fewer characters than the field width, it will be padded on the left (or right, if the left-adjustment flag (-), described below, has been given) to the field width.

An optional precision that gives the minimum number of digits to appear number of digits to appear after the decimal-point character for the e, E, and f conversions, the maximum number of significant digits for the g and G conversions.

The precision takes the form of a period (.) followed by a decimal digit string; a null digit string is treated as zero. Padding specified by the precision overrides the padding specified by the field width.

A conversion character (see below) that indicates the type of conversion to be applied.

A field width or precision may be indicated by an asterisk (*) instead of a digit string. In this case, an integer args supplies the field width or precision. The args that is actually converted is not fetched until the conversion letter is seen, so the args specifying field width or precision must appear before the args (if any) to be converted. If the precision argument is negative, it will be changed to zero. A negative field width argument is taken as a - flag, followed by a positive field width.

In format strings containing the *digits$ form of a conversion specification, a field width or precision may also be indicated by the sequence *digits$, giving the position in the argument list of an integer args containing the field width or precision.

When numbered argument specifications are used, specifying the Nth argument requires that all the leading arguments, from the first to the (N-1)th, be specified in the format string.

The flag characters and their meanings are:

-

The result of the conversion will be left-justified within the field. (It will be right-justified if this flag is not specified.)

+

The result of a signed conversion will always begin with a sign (+ or -). (It will begin with a sign only when a negative value is converted if this flag is not specified.)

space

If the first character of a signed conversion is not a sign, a space will be placed before the result. This means that if the space and + flags both appear, the space flag will be ignored.

#

The value is to be converted to an alternate form. For e, E, f, g, and G conversions, the result will always contain a decimal-point character, even if no digits follow the point (normally, a decimal point appears in the result of these conversions only if a digit follows it). For g and G conversions, trailing zeros will not be removed from the result as they normally are.

0

For e, E, f, g, and G conversions, leading zeros (following any indication of sign or base) are used to pad to the field width; no space padding is performed. If the 0 and flags both appear, the 0 flag will be ignored.

Each conversion character results in fetching zero or more args. The results are undefined if there are insufficient args for the format. If the format is exhausted while args remain, the excess args are ignored.

The conversion characters and their meanings are:

f

The double args is converted to decimal notation in the style [ - ]ddd.ddd, where the number of digits after the decimal-point character (see setlocale(3C)) is equal to the precision specification. If the precision is omitted from arg, six digits are output; if the precision is explicitly zero and the # flag is not specified, no decimal-point character appears. If a decimal-point character appears, at least 1 digit appears before it. The value is rounded to the appropriate number of digits.

e,E

The double args is converted to the style [ - ]d.ddde + dd, where there is one digit before the decimal-point character (which is non- zero if the argument is non-zero) and the number of digits after it is equal to the precision. When the precision is missing, six digits are produced; if the precision is zero and the # flag is not specified, no decimal-point character appears. The E conversion character will produce a number with E instead of e introducing the exponent. The exponent always contains at least two digits. The value is rounded to the appropriate number of digits.

g,G

The double args is printed in style f or e (or in style E in the case of a G conversion character), with the precision specifying the number of significant digits. If the precision is zero, it is taken as one. The style used depends on the value converted: style e (or E) will be used only if the exponent resulting from the conversion is less than -4 or greater than or equal to the precision. Trailing zeros are removed from the fractional part of the result. A decimal-point character appears only if it is followed by a digit.

%

Print a %; no argument is converted.

If the character after the % or %digits$ sequence is not a valid conversion character, the results of the conversion are undefined.

If a floating-point value is the internal representation for infinity, the output is [ + ]Infinity, where Infinity is either Infinity or Inf, depending on the desired output string length. Printing of the sign follows the rules described above.

If a floating-point value is the internal representation for ``not-a-number,'' the output is [+]NaN. Printing of the sign follows the rules described above.

In no case does a non-existent or small field width cause truncation of a field; if the result of a conversion is wider than the field width, the field is simply expanded to contain the conversion result.