___________________________
format − Format a string in the style of sprintf
format formatString ?arg arg ...? ___________________________
This command generates a formatted string in a fashion similar to the ANSI C sprintf procedure. 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.
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 character is a % then it is not copied to the result string. Instead, the characters following the % character are treated as a conversion specifier. The conversion specifier controls 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 specifier, a set of flags, a minimum field width, a precision, a size modifier, and a conversion 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.
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 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 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. | ||
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 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 %. |
The behavior of the format command is the same as the ANSI C sprintf procedure except for the following differences:
[1] |
Tcl guarantees that it will be working with UNICODE characters. | ||
[2] |
%p and %n specifiers are not supported. | ||
[3] |
For %c conversions the argument must be an integer value, which will then be converted to the corresponding character value. | ||
[4] |
The size modifiers are ignored when formatting floating-point values. The ll modifier has no sprintf counterpart. The b specifier has no sprintf counterpart. |
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 format:
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
scan(n), sprintf(3), string(3)
conversion specifier, format, sprintf, string, substitution
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