1format(n) Tcl Built-In Commands format(n)
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8 format - Format a string in the style of sprintf
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11 format formatString ?arg arg ...?
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16 This command generates a formatted string in the same way as the ANSI C
17 sprintf procedure (it uses sprintf in its implementation). Format‐
18 String indicates how to format the result, using % conversion speci‐
19 fiers as in sprintf, and the additional arguments, if any, provide val‐
20 ues to be substituted into the result. The return value from format is
21 the formatted string.
22
24 The command operates by scanning formatString from left to right. Each
25 character from the format string is appended to the result string
26 unless it is a percent sign. If the character is a % then it is not
27 copied to the result string. Instead, the characters following the %
28 character are treated as a conversion specifier. The conversion speci‐
29 fier controls the conversion of the next successive arg to a particular
30 format and the result is appended to the result string in place of the
31 conversion specifier. If there are multiple conversion specifiers in
32 the format string, then each one controls the conversion of one addi‐
33 tional arg. The format command must be given enough args to meet the
34 needs of all of the conversion specifiers in formatString.
35 Each conversion specifier may contain up to six different parts: an
37 XPG3 position specifier, a set of flags, a minimum field width, a pre‐
38 cision, a length modifier, and a conversion character. Any of these
39 fields may be omitted except for the conversion character. The fields
40 that are present must appear in the order given above. The paragraphs
41 below discuss each of these fields in turn.
42 If the % is followed by a decimal number and a $, as in ``%2$d'', then
44 the value to convert is not taken from the next sequential argument.
45 Instead, it is taken from the argument indicated by the number, where 1
46 corresponds to the first arg. If the conversion specifier requires
47 multiple arguments because of * characters in the specifier then suc‐
48 cessive arguments are used, starting with the argument given by the
49 number. This follows the XPG3 conventions for positional specifiers.
50 If there are any positional specifiers in formatString then all of the
51 specifiers must be positional.
52 The second portion of a conversion specifier may contain any of the
54 following flag characters, in any order:
55 - Specifies that the converted argument should be left-justi‐
57 fied in its field (numbers are normally right-justified with
58 leading spaces if needed).
59 + Specifies that a number should always be printed with a sign,
61 even if positive.
62 space Specifies that a space should be added to the beginning of
64 the number if the first character isn't a sign.
65 0 Specifies that the number should be padded on the left with
67 zeroes instead of spaces.
68 # Requests an alternate output form. For o and O conversions it
70 guarantees that the first digit is always 0. For x or X con‐
71 versions, 0x or 0X (respectively) will be added to the begin‐
72 ning of the result unless it is zero. For all floating-point
73 conversions (e, E, f, g, and G) it guarantees that the result
74 always has a decimal point. For g and G conversions it spec‐
75 ifies that trailing zeroes should not be removed.
76 The third portion of a conversion specifier is a number giving a mini‐
78 mum field width for this conversion. It is typically used to make col‐
79 umns line up in tabular printouts. If the converted argument contains
80 fewer characters than the minimum field width then it will be padded so
81 that it is as wide as the minimum field width. Padding normally occurs
82 by adding extra spaces on the left of the converted argument, but the 0
83 and - flags may be used to specify padding with zeroes on the left or
84 with spaces on the right, respectively. If the minimum field width is
85 specified as * rather than a number, then the next argument to the for‐
86 mat command determines the minimum field width; it must be a numeric
87 string.
88 The fourth portion of a conversion specifier is a precision, which con‐
90 sists of a period followed by a number. The number is used in differ‐
91 ent ways for different conversions. For e, E, and f conversions it
92 specifies the number of digits to appear to the right of the decimal
93 point. For g and G conversions it specifies the total number of digits
94 to appear, including those on both sides of the decimal point (however,
95 trailing zeroes after the decimal point will still be omitted unless
96 the # flag has been specified). For integer conversions, it specifies
97 a minimum number of digits to print (leading zeroes will be added if
98 necessary). For s conversions it specifies the maximum number of char‐
99 acters to be printed; if the string is longer than this then the trail‐
100 ing characters will be dropped. If the precision is specified with *
101 rather than a number then the next argument to the format command
102 determines the precision; it must be a numeric string.
103 The fifth part of a conversion specifier is a length modifier, which
105 must be h or l. If it is h it specifies that the numeric value should
106 be truncated to a 16-bit value before converting. This option is
107 rarely useful. If it is l it specifies that the numeric value should │
108 be (at least) a 64-bit value. If neither h nor l are present, numeric │
109 values are interpreted as being values of the width of the native │
110 machine word, as described by tcl_platform(wordSize).
111 The last thing in a conversion specifier is an alphabetic character
113 that determines what kind of conversion to perform. The following con‐
114 version characters are currently supported:
115 d Convert integer to signed decimal string.
117 u Convert integer to unsigned decimal string.
119 i Convert integer to signed decimal string; the integer may
121 either be in decimal, in octal (with a leading 0) or in hexa‐
122 decimal (with a leading 0x).
123 o Convert integer to unsigned octal string.
125 x or X Convert integer to unsigned hexadecimal string, using digits
127 ``0123456789abcdef'' for x and ``0123456789ABCDEF'' for X). │
128 c │
130 Convert integer to the Unicode character it represents.
131 s No conversion; just insert string.
133 f Convert floating-point number to signed decimal string of the
135 form xx.yyy, where the number of y's is determined by the
136 precision (default: 6). If the precision is 0 then no deci‐
137 mal point is output.
138 e or e Convert floating-point number to scientific notation in the
140 form x.yyye±zz, where the number of y's is determined by the
141 precision (default: 6). If the precision is 0 then no deci‐
142 mal point is output. If the E form is used then E is printed
143 instead of e.
144 g or G If the exponent is less than -4 or greater than or equal to
146 the precision, then convert floating-point number as for %e
147 or %E. Otherwise convert as for %f. Trailing zeroes and a
148 trailing decimal point are omitted.
149 % No conversion: just insert %.
151 For the numerical conversions the argument being converted must be an
153 integer or floating-point string; format converts the argument to
154 binary and then converts it back to a string according to the conver‐
155 sion specifier.
156
158 The behavior of the format command is the same as the ANSI C sprintf
159 procedure except for the following differences:
160 [1] %p and %n specifiers are not currently supported.
162 [2] For %c conversions the argument must be a decimal string, which
164 will then be converted to the corresponding character value.
165 [3] The l modifier is ignored for real values and on 64-bit plat‐ │
167 forms, which are always converted as if the l modifier were │
168 present (i.e. the types double and long are used for the inter‐ │
169 nal representation of real and integer values, respectively).
170 If the h modifier is specified then integer values are truncated
171 to short before conversion. Both h and l modifiers are ignored
172 on all other conversions.
173
175 Convert the output of time into seconds to an accuracy of hundredths of
176 a second:
177 set us [lindex [time $someTclCode] 0]
178 puts [format "%.2f seconds to execute" [expr {$us / 1e6}]]
179 Create a packed X11 literal color specification:
181 # Each color-component should be in range (0..255)
182 set color [format "#%02x%02x%02x" $r $g $b]
183 Use XPG3 format codes to allow reordering of fields (a technique that
185 is often used in localized message catalogs; see msgcat) without
186 reordering the data values passed to format:
187 set fmt1 "Today, %d shares in %s were bought at $%.2f each"
188 puts [format $fmt1 123 "Global BigCorp" 19.37]
189 set fmt2 "Bought %2\$s equity ($%3$.2f x %1\$d) today"
191 puts [format $fmt2 123 "Global BigCorp" 19.37]
192 Print a small table of powers of three:
194 # Set up the column widths
195 set w1 5
196 set w2 10
197 # Make a nice header (with separator) for the table first
199 set sep +-[string repeat - $w1]-+-[string repeat - $w2]-+
200 puts $sep
201 puts [format "| %-*s | %-*s |" $w1 "Index" $w2 "Power"]
202 puts $sep
203 # Print the contents of the table
205 set p 1
206 for {set i 0} {$i<=20} {incr i} {
207 puts [format "| %*d | %*ld |" $w1 $i $w2 $p]
208 set p [expr {wide($p) * 3}]
209 }
210 # Finish off by printing the separator again
212 puts $sep
213
216 scan(n), sprintf(3), string(n)
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220 conversion specifier, format, sprintf, string, substitution
221Tcl 8.1 format(n)