Number Formatting Options

A format specification, which consists of optional and required fields, has the following form:

%[flags] [width] [.precision] type

for example, if an edit control had the following formatting:

%04.0f

loading the number '7' into it will display '0007'.

Each field of the format specification is a single character or a number signifying a particular format option. The simplest format specification contains only the percent sign and a type character (for example, %s ). If a percent sign is followed by a character that has no meaning as a format field, the character is copied to stdout . For example, to print a percent-sign character, use %% .

The optional fields, which appear before the type character, control other aspects of the formatting, as follows:

type

Required character that determines whether the associated argument is interpreted as a character, a string, or a number

Character	Type	Output Format
d	int	Signed decimal integer.
x	int	Unsigned hexadecimal integer, using abcdef.
X	int	Unsigned hexadecimal integer, using ABCDEF.
e	double	Signed value having the form [ ] d . dddd e [ sign ] ddd where d is a single decimal digit, dddd is one or more decimal digits, ddd is exactly three decimal digits, and sign is + or .
E	double	Identical to the e format except that E rather than e introduces the exponent.
f	double	Signed value having the form [ ] dddd . dddd , where dddd is one or more decimal digits. The number of digits before the decimal point depends on the magnitude of the number, and the number of digits after the decimal point depends on the requested precision.

flags

Optional character or characters that control justification of output and printing of signs, blanks, decimal points, and octal and hexadecimal prefixes (see below). More than one flag can appear in a format specification.

The first optional field of the format specification is flags . A flag directive is a character that justifies output and prints signs, blanks, decimal points, and octal and hexadecimal prefixes. More than one flag directive may appear in a format specification.

Flag	Meaning	Default
	Left align the result within the given field width.	Right align.
+	Prefix the output value with a sign (+ or ) if the output value is of a signed type.	Sign appears only for negative signed values ().
0	If width is prefixed with 0 , zeros are added until the minimum width is reached. If 0 and appear, the 0 is ignored. If 0 is specified with an integer format ( i , u , x , X , o , d ) the 0 is ignored.	No padding.
blank (' ')	Prefix the output value with a blank if the output value is signed and positive; the blank is ignored if both the blank and + flags appear.	No blank appears.
#	When used with the o , x , or X format, the # flag prefixes any nonzero output value with 0, 0x, or 0X, respectively.	No blank appears.
	When used with the e , E , or f format, the # flag forces the output value to contain a decimal point in all cases.	Decimal point appears only if digits follow it.
	When used with the g or G format, the # flag forces the output value to contain a decimal point in all cases and prevents the truncation of trailing zeros. Ignored when used with c , d , i , u , or s .	Decimal point appears only if digits follow it. Trailing zeros are truncated.

width
Optional number that specifies the minimum number of characters output.

precision

Optional number that specifies the maximum number of characters printed for all or part of the output field, or the minimum number of digits printed for integer values (see below).

Type	Meaning	Default
c, C	The precision has no effect.	Character is printed.
d, i, u, o, x, X	The precision specifies the minimum number of digits to be printed. If the number of digits in the argument is less than precision , the output value is padded on the left with zeros. The value is not truncated when the number of digits exceeds precision .	Default precision is 1.
e, E	The precision specifies the number of digits to be printed after the decimal point. The last printed digit is rounded.	Default precision is 6; if precision is 0 or the period (.) appears without a number following it, no decimal point is printed.
f	The precision value specifies the number of digits after the decimal point. If a decimal point appears, at least one digit appears before it. The value is rounded to the appropriate number of digits.	Default precision is 6; if precision is 0, or if the period (.) appears without a number following it, no decimal point is printed.
g, G	The precision specifies the maximum number of significant digits printed.	Six significant digits are printed, with any trailing zeros truncated.