FormatString:
    FormatStringItem*
FormatStringItem:
    '%%'
    '%' Position Flags Width Precision FormatChar
    '%(' FormatString '%)'
    OtherCharacterExceptPercent
Position:
    empty
    Integer '$'
Flags:
    empty
    '-' Flags
    '+' Flags
    '#' Flags
    '0' Flags
    ' ' Flags
Width:
    empty
    Integer
    '*'
Precision:
    empty
    '.'
    '.' Integer
    '.*'
Integer:
    Digit
    Digit Integer
Digit:
    '0'|'1'|'2'|'3'|'4'|'5'|'6'|'7'|'8'|'9'
FormatChar:
    's'|'c'|'b'|'d'|'o'|'x'|'X'|'e'|'E'|'f'|'F'|'g'|'G'|'a'|'A'

's'

The corresponding argument is formatted in a manner consistent with its type:

bool

The result is 'true' or 'false'.

integral types

The %d format is used.

floating point types

The %g format is used.

string types

The result is the string converted to UTF-8. A Precision specifies the maximum number of characters to use in the result.

classes derived from Object

The result is the string returned from the class instance's .toString() method. A Precision specifies the maximum number of characters to use in the result.

non-string static and dynamic arrays

The result is [s₀, s₁, ...] where s_k is the kth element formatted with the default format.

'c'

The corresponding argument must be a character type.

'b','d','o','x','X'

The corresponding argument must be an integral type and is formatted as an integer. If the argument is a signed type and the FormatChar is d it is converted to a signed string of characters, otherwise it is treated as unsigned. An argument of type bool is formatted as '1' or '0'. The base used is binary for b, octal for o, decimal for d, and hexadecimal for x or X. x formats using lower case letters, X uppercase. If there are fewer resulting digits than the Precision, leading zeros are used as necessary. If the Precision is 0 and the number is 0, no digits result.

'e','E'

A floating point number is formatted as one digit before the decimal point, Precision digits after, the FormatChar, ±, followed by at least a two digit exponent: d.dddddde±dd. If there is no Precision, six digits are generated after the decimal point. If the Precision is 0, no decimal point is generated.

'f','F'

A floating point number is formatted in decimal notation. The Precision specifies the number of digits generated after the decimal point. It defaults to six. At least one digit is generated before the decimal point. If the Precision is zero, no decimal point is generated.

'g','G'

A floating point number is formatted in either e or f format for g; E or F format for G. The f format is used if the exponent for an e format is greater than -5 and less than the Precision. The Precision specifies the number of significant digits, and defaults to six. Trailing zeros are elided after the decimal point, if the fractional part is zero then no decimal point is generated.

'a','A'

A floating point number is formatted in hexadecimal exponential notation 0xh.hhhhhhp±d. There is one hexadecimal digit before the decimal point, and as many after as specified by the Precision. If the Precision is zero, no decimal point is generated. If there is no Precision, as many hexadecimal digits as necessary to exactly represent the mantissa are generated. The exponent is written in as few digits as possible, but at least one, is in decimal, and represents a power of 2 as in h.hhhhhh*2^±d. The exponent for zero is zero. The hexadecimal digits, x and p are in upper case if the FormatChar is upper case.

string s = "hello!124:34.5";
string a;
int b;
double c;
formattedRead(s, "%s!%s:%s", &a, &b, &c);
assert(a == "hello" && b == 124 && c == 34.5);

auto a = appender!(string)();
auto fmt = "Number: %2.4e\nString: %s";
auto f = FormatSpec!char(fmt);

f.writeUpToNextSpec(a);

assert(a.data == "Number: ");
assert(f.trailing == "\nString: %s");
assert(f.spec == 'e');
assert(f.width == 2);
assert(f.precision == 4);

f.writeUpToNextSpec(a);

assert(a.data == "Number: \nString: ");
assert(f.trailing == "");
assert(f.spec == 's');

• void[] is formatted like ubyte[].
• Const array is converted to input range by removing its qualifier.