OPTIONAL POSITIONAL SPECIFIER¶

If the % is followed by a decimal number and a $, as in “%2$d”, then the value to convert is not taken from the next sequential argument. Instead, it is taken from the argument indicated by the number, where 1 corresponds to the first arg. If the conversion specifier requires multiple arguments because of * characters in the specifier then successive arguments are used, starting with the argument given by the number. This follows the XPG3 conventions for positional specifiers. If there are any positional specifiers in formatString then all of the specifiers must be positional.

OPTIONAL FLAGS¶

The second portion of a conversion specifier may contain any of the following flag characters, in any order:

-

Specifies that the converted argument should be left-justified in its field (numbers are normally right-justified with leading spaces if needed).

+

Specifies that a number should always be printed with a sign, even if positive.

space

Specifies that a space should be added to the beginning of the number if the first character is not a sign.

0

Specifies that the number should be padded on the left with zeroes instead of spaces.

#

Requests an alternate output form. For o conversions it guarantees that the first digit is always 0. For x or X conversions, 0x or 0X (respectively) will be added to the beginning of the result unless it is zero. For b conversions, 0b will be added to the beginning of the result unless it is zero. For all floating-point conversions (e, E, f, g, and G) it guarantees that the result always has a decimal point. For g and G conversions it specifies that trailing zeroes should not be removed.

OPTIONAL FIELD WIDTH¶

The third portion of a conversion specifier is a decimal number giving a minimum field width for this conversion. It is typically used to make columns line up in tabular printouts. If the converted argument contains fewer characters than the minimum field width then it will be padded so that it is as wide as the minimum field width. Padding normally occurs by adding extra spaces on the left of the converted argument, but the 0 and - flags may be used to specify padding with zeroes on the left or with spaces on the right, respectively. If the minimum field width is specified as * rather than a number, then the next argument to the format command determines the minimum field width; it must be an integer value.

OPTIONAL PRECISION/BOUND¶

The fourth portion of a conversion specifier is a precision, which consists of a period followed by a number. The number is used in different ways for different conversions. For e, E, and f conversions it specifies the number of digits to appear to the right of the decimal point. For g and G conversions it specifies the total number of digits to appear, including those on both sides of the decimal point (however, trailing zeroes after the decimal point will still be omitted unless the # flag has been specified). For integer conversions, it specifies a minimum number of digits to print (leading zeroes will be added if necessary). For s conversions it specifies the maximum number of characters to be printed; if the string is longer than this then the trailing characters will be dropped. If the precision is specified with * rather than a number then the next argument to the format command determines the precision; it must be a numeric string.

OPTIONAL SIZE MODIFIER¶

The fifth part of a conversion specifier is a size modifier, which must be ll, h, or l. If it is ll it specifies that an integer value is taken without truncation for conversion to a formatted substring. If it is h it specifies that an integer value is truncated to a 16-bit range before converting. This option is rarely useful. If it is l it specifies that the integer value is truncated to the same range as that produced by the wide() function of the expr command (at least a 64-bit range). If neither h nor l are present, the integer value is truncated to the same range as that produced by the int() function of the expr command (at least a 32-bit range, but determined by the value of the wordSize element of the tcl_platform array).

MANDATORY CONVERSION TYPE¶

The last thing in a conversion specifier is an alphabetic character that determines what kind of conversion to perform. The following conversion characters are currently supported:

d

Convert integer to signed decimal string.

u

Convert integer to unsigned decimal string. The conversion makes no sense without reference to a truncation range, so the size modifier ll is not permitted in combination with conversion character u.

i

Convert integer to signed decimal string (equivalent to d).

o

Convert integer to unsigned octal string.

x or X

Convert integer to unsigned hexadecimal string, using digits “0123456789abcdef” for x and “0123456789ABCDEF” for X).

b

Convert integer to unsigned binary string, using digits 0 and 1.

c

Convert integer to the Unicode character it represents.

s

No conversion; just insert string.

f

Convert number to signed decimal string of the form xx.yyy, where the number of y's is determined by the precision (default: 6). If the precision is 0 then no decimal point is output.

e or E

Convert number to scientific notation in the form x.yyye±zz, where the number of y's is determined by the precision (default: 6). If the precision is 0 then no decimal point is output. If the E form is used then E is printed instead of e.

g or G

If the exponent is less than -4 or greater than or equal to the precision, then convert number as for %e or %E. Otherwise convert as for %f. Trailing zeroes and a trailing decimal point are omitted.

%

No conversion: just insert %.