format(n) - phpMan

format(n) Tcl Built-In Commands format(n)

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NAME
format - Format a string in the style of sprintf

SYNOPSIS
format formatString ?arg arg ...?
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INTRODUCTION
This command generates a formatted string in a fashion similar to the ANSI C sprintf pro-
cedure. FormatString indicates how to format the result, using % conversion specifiers as
in sprintf, and the additional arguments, if any, provide values to be substituted into
the result. The return value from format is the formatted string.

DETAILS ON FORMATTING
The command operates by scanning formatString from left to right. Each character from the
format string is appended to the result string unless it is a percent sign. If the char-
acter is a % then it is not copied to the result string. Instead, the characters follow-
ing the % character are treated as a conversion specifier. The conversion specifier con-
trols the conversion of the next successive arg to a particular format and the result is
appended to the result string in place of the conversion specifier. If there are multiple
conversion specifiers in the format string, then each one controls the conversion of one
additional arg. The format command must be given enough args to meet the needs of all of
the conversion specifiers in formatString.

Each conversion specifier may contain up to six different parts: an XPG3 position speci-
fier, a set of flags, a minimum field width, a precision, a size modifier, and a conver-
sion character. Any of these fields may be omitted except for the conversion character.
The fields that are present must appear in the order given above. The paragraphs below
discuss each of these fields in turn.

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 speci-
fier 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 format-
String then all of the specifiers must be positional.

The second portion of a conversion specifier may contain any of the following flag charac-
ters, 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 and 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 all float-
ing-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.

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 print-
outs. 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.

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 inte-
ger 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.

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() func-
tion 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 tcl_platform(word-
Size)).

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 sup-
ported:

d Convert integer to signed decimal string.

u Convert integer to unsigned decimal string.

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).

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 %.

DIFFERENCES FROM ANSI SPRINTF
The behavior of the format command is the same as the ANSI C sprintf procedure except for
the following differences:

[1] %p and %n specifiers are not supported.

[2] For %c conversions the argument must be an integer value, which will then be con-
verted to the corresponding character value.

[3] The size modifiers are ignored when formatting floating-point values. The ll modi-
fier has no sprintf counterpart.

EXAMPLES
Convert the numeric value of a UNICODE character to the character itself:
set value 120
set char [format %c $value]

Convert the output of time into seconds to an accuracy of hundredths of a second:
set us [lindex [time $someTclCode] 0]
puts [format "%.2f seconds to execute" [expr {$us / 1e6}]]

Create a packed X11 literal color specification:
# Each color-component should be in range (0..255)
set color [format "#%02x%02x%02x" $r $g $b]

Use XPG3 format codes to allow reordering of fields (a technique that is often used in
localized message catalogs; see msgcat) without reordering the data values passed to for-
mat:
set fmt1 "Today, %d shares in %s were bought at $%.2f each"
puts [format $fmt1 123 "Global BigCorp" 19.37]

set fmt2 "Bought %2\$s equity ($%3$.2f x %1\$d) today"
puts [format $fmt2 123 "Global BigCorp" 19.37]

Print a small table of powers of three:
# Set up the column widths
set w1 5
set w2 10

# Make a nice header (with separator) for the table first
set sep +-[string repeat - $w1]-+-[string repeat - $w2]-+
puts $sep
puts [format "| %-*s | %-*s |" $w1 "Index" $w2 "Power"]
puts $sep

# Print the contents of the table
set p 1
for {set i 0} {$i<=20} {incr i} {
puts [format "| %*d | %*ld |" $w1 $i $w2 $p]
set p [expr {wide($p) * 3}]
}

# Finish off by printing the separator again
puts $sep