format(3Tcl) format(3Tcl)
format - Format a string in the style of sprintf
format formatString ?arg arg ...?
This command generates a formatted string in the same way as the ANSI C
sprintf procedure (it uses sprintf in its implementation). 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 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
length 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.
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.
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).
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format(3Tcl) format(3Tcl)
+ 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 isn't 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 floatingpoint
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 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 a numeric string.
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.
The fifth part of a conversion specifier is a length modifier, which must
be h or l. If it is h it specifies that the numeric value should be
truncated to a 16-bit value before converting. This option is rarely
useful. The l modifier is ignored.
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:
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format(3Tcl) format(3Tcl)
d Convert integer to signed decimal string.
u Convert integer to unsigned decimal string.
i Convert integer to signed decimal string; the integer may
either be in decimal, in octal (with a leading 0) or in
hexadecimal (with a leading 0x).
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 8-bit character it represents.
s No conversion; just insert string.
f Convert floating-point 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 floating-point 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 floating-point number as for %e or %E.
Otherwise convert as for %f. Trailing zeroes and a trailing
decimal point are omitted.
% No conversion: just insert %.
For the numerical conversions the argument being converted must be an
integer or floating-point string; format converts the argument to binary
and then converts it back to a string according to the conversion
specifier.
DIFFERENCES FROM ANSI SPRINTF [Toc] [Back] 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 currently supported. |
[2] For %c conversions the argument must be a decimal string, which will
then be converted to the corresponding character value.
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format(3Tcl) format(3Tcl)
[3] The l modifier is ignored; integer values are always converted as |
if there were no modifier present and real values are always |
converted as if the l modifier were present (i.e. type double is |
used for the internal representation). If the h modifier is |
specified then integer values are truncated to short before |
conversion.
conversion specifier, format, sprintf, string, substitution
PPPPaaaaggggeeee 4444 [ Back ]
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