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*: transfer back to cmake from autotools autotools just made lots of things more complicated than they should have and many things broke (i.e. translations)
author Paper <paper@paper.us.eu.org>
date Thu, 20 Jun 2024 05:56:06 -0400
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342:adb79bdde329 343:1faa72660932
1 .. _syntax:
2
3 ********************
4 Format String Syntax
5 ********************
6
7 Formatting functions such as :ref:`fmt::format() <format>` and
8 :ref:`fmt::print() <print>` use the same format string syntax described in this
9 section.
10
11 Format strings contain "replacement fields" surrounded by curly braces ``{}``.
12 Anything that is not contained in braces is considered literal text, which is
13 copied unchanged to the output. If you need to include a brace character in the
14 literal text, it can be escaped by doubling: ``{{`` and ``}}``.
15
16 The grammar for a replacement field is as follows:
17
18 .. productionlist:: sf
19 replacement_field: "{" [`arg_id`] [":" (`format_spec` | `chrono_format_spec`)] "}"
20 arg_id: `integer` | `identifier`
21 integer: `digit`+
22 digit: "0"..."9"
23 identifier: `id_start` `id_continue`*
24 id_start: "a"..."z" | "A"..."Z" | "_"
25 id_continue: `id_start` | `digit`
26
27 In less formal terms, the replacement field can start with an *arg_id*
28 that specifies the argument whose value is to be formatted and inserted into
29 the output instead of the replacement field.
30 The *arg_id* is optionally followed by a *format_spec*, which is preceded by a
31 colon ``':'``. These specify a non-default format for the replacement value.
32
33 See also the :ref:`formatspec` section.
34
35 If the numerical arg_ids in a format string are 0, 1, 2, ... in sequence,
36 they can all be omitted (not just some) and the numbers 0, 1, 2, ... will be
37 automatically inserted in that order.
38
39 Named arguments can be referred to by their names or indices.
40
41 Some simple format string examples::
42
43 "First, thou shalt count to {0}" // References the first argument
44 "Bring me a {}" // Implicitly references the first argument
45 "From {} to {}" // Same as "From {0} to {1}"
46
47 The *format_spec* field contains a specification of how the value should be
48 presented, including such details as field width, alignment, padding, decimal
49 precision and so on. Each value type can define its own "formatting
50 mini-language" or interpretation of the *format_spec*.
51
52 Most built-in types support a common formatting mini-language, which is
53 described in the next section.
54
55 A *format_spec* field can also include nested replacement fields in certain
56 positions within it. These nested replacement fields can contain only an
57 argument id; format specifications are not allowed. This allows the formatting
58 of a value to be dynamically specified.
59
60 See the :ref:`formatexamples` section for some examples.
61
62 .. _formatspec:
63
64 Format Specification Mini-Language
65 ==================================
66
67 "Format specifications" are used within replacement fields contained within a
68 format string to define how individual values are presented (see
69 :ref:`syntax`). Each formattable type may define how the format
70 specification is to be interpreted.
71
72 Most built-in types implement the following options for format specifications,
73 although some of the formatting options are only supported by the numeric types.
74
75 The general form of a *standard format specifier* is:
76
77 .. productionlist:: sf
78 format_spec: [[`fill`]`align`][`sign`]["#"]["0"][`width`]["." `precision`]["L"][`type`]
79 fill: <a character other than '{' or '}'>
80 align: "<" | ">" | "^"
81 sign: "+" | "-" | " "
82 width: `integer` | "{" [`arg_id`] "}"
83 precision: `integer` | "{" [`arg_id`] "}"
84 type: "a" | "A" | "b" | "B" | "c" | "d" | "e" | "E" | "f" | "F" | "g" | "G" |
85 : "o" | "p" | "s" | "x" | "X" | "?"
86
87 The *fill* character can be any Unicode code point other than ``'{'`` or
88 ``'}'``. The presence of a fill character is signaled by the character following
89 it, which must be one of the alignment options. If the second character of
90 *format_spec* is not a valid alignment option, then it is assumed that both the
91 fill character and the alignment option are absent.
92
93 The meaning of the various alignment options is as follows:
94
95 +---------+----------------------------------------------------------+
96 | Option | Meaning |
97 +=========+==========================================================+
98 | ``'<'`` | Forces the field to be left-aligned within the available |
99 | | space (this is the default for most objects). |
100 +---------+----------------------------------------------------------+
101 | ``'>'`` | Forces the field to be right-aligned within the |
102 | | available space (this is the default for numbers). |
103 +---------+----------------------------------------------------------+
104 | ``'^'`` | Forces the field to be centered within the available |
105 | | space. |
106 +---------+----------------------------------------------------------+
107
108 Note that unless a minimum field width is defined, the field width will always
109 be the same size as the data to fill it, so that the alignment option has no
110 meaning in this case.
111
112 The *sign* option is only valid for floating point and signed integer types,
113 and can be one of the following:
114
115 +---------+------------------------------------------------------------+
116 | Option | Meaning |
117 +=========+============================================================+
118 | ``'+'`` | indicates that a sign should be used for both |
119 | | nonnegative as well as negative numbers. |
120 +---------+------------------------------------------------------------+
121 | ``'-'`` | indicates that a sign should be used only for negative |
122 | | numbers (this is the default behavior). |
123 +---------+------------------------------------------------------------+
124 | space | indicates that a leading space should be used on |
125 | | nonnegative numbers, and a minus sign on negative numbers. |
126 +---------+------------------------------------------------------------+
127
128 The ``'#'`` option causes the "alternate form" to be used for the
129 conversion. The alternate form is defined differently for different
130 types. This option is only valid for integer and floating-point types.
131 For integers, when binary, octal, or hexadecimal output is used, this
132 option adds the prefix respective ``"0b"`` (``"0B"``), ``"0"``, or
133 ``"0x"`` (``"0X"``) to the output value. Whether the prefix is
134 lower-case or upper-case is determined by the case of the type
135 specifier, for example, the prefix ``"0x"`` is used for the type ``'x'``
136 and ``"0X"`` is used for ``'X'``. For floating-point numbers the
137 alternate form causes the result of the conversion to always contain a
138 decimal-point character, even if no digits follow it. Normally, a
139 decimal-point character appears in the result of these conversions
140 only if a digit follows it. In addition, for ``'g'`` and ``'G'``
141 conversions, trailing zeros are not removed from the result.
142
143 .. ifconfig:: False
144
145 The ``','`` option signals the use of a comma for a thousands separator.
146 For a locale aware separator, use the ``'L'`` integer presentation type
147 instead.
148
149 *width* is a decimal integer defining the minimum field width. If not
150 specified, then the field width will be determined by the content.
151
152 Preceding the *width* field by a zero (``'0'``) character enables sign-aware
153 zero-padding for numeric types. It forces the padding to be placed after the
154 sign or base (if any) but before the digits. This is used for printing fields in
155 the form '+000000120'. This option is only valid for numeric types and it has no
156 effect on formatting of infinity and NaN.
157
158 The *precision* is a decimal number indicating how many digits should be
159 displayed after the decimal point for a floating-point value formatted with
160 ``'f'`` and ``'F'``, or before and after the decimal point for a floating-point
161 value formatted with ``'g'`` or ``'G'``. For non-number types the field
162 indicates the maximum field size - in other words, how many characters will be
163 used from the field content. The *precision* is not allowed for integer,
164 character, Boolean, and pointer values. Note that a C string must be
165 null-terminated even if precision is specified.
166
167 The ``'L'`` option uses the current locale setting to insert the appropriate
168 number separator characters. This option is only valid for numeric types.
169
170 Finally, the *type* determines how the data should be presented.
171
172 The available string presentation types are:
173
174 +---------+----------------------------------------------------------+
175 | Type | Meaning |
176 +=========+==========================================================+
177 | ``'s'`` | String format. This is the default type for strings and |
178 | | may be omitted. |
179 +---------+----------------------------------------------------------+
180 | ``'?'`` | Debug format. The string is quoted and special |
181 | | characters escaped. |
182 +---------+----------------------------------------------------------+
183 | none | The same as ``'s'``. |
184 +---------+----------------------------------------------------------+
185
186 The available character presentation types are:
187
188 +---------+----------------------------------------------------------+
189 | Type | Meaning |
190 +=========+==========================================================+
191 | ``'c'`` | Character format. This is the default type for |
192 | | characters and may be omitted. |
193 +---------+----------------------------------------------------------+
194 | ``'?'`` | Debug format. The character is quoted and special |
195 | | characters escaped. |
196 +---------+----------------------------------------------------------+
197 | none | The same as ``'c'``. |
198 +---------+----------------------------------------------------------+
199
200 The available integer presentation types are:
201
202 +---------+----------------------------------------------------------+
203 | Type | Meaning |
204 +=========+==========================================================+
205 | ``'b'`` | Binary format. Outputs the number in base 2. Using the |
206 | | ``'#'`` option with this type adds the prefix ``"0b"`` |
207 | | to the output value. |
208 +---------+----------------------------------------------------------+
209 | ``'B'`` | Binary format. Outputs the number in base 2. Using the |
210 | | ``'#'`` option with this type adds the prefix ``"0B"`` |
211 | | to the output value. |
212 +---------+----------------------------------------------------------+
213 | ``'c'`` | Character format. Outputs the number as a character. |
214 +---------+----------------------------------------------------------+
215 | ``'d'`` | Decimal integer. Outputs the number in base 10. |
216 +---------+----------------------------------------------------------+
217 | ``'o'`` | Octal format. Outputs the number in base 8. |
218 +---------+----------------------------------------------------------+
219 | ``'x'`` | Hex format. Outputs the number in base 16, using |
220 | | lower-case letters for the digits above 9. Using the |
221 | | ``'#'`` option with this type adds the prefix ``"0x"`` |
222 | | to the output value. |
223 +---------+----------------------------------------------------------+
224 | ``'X'`` | Hex format. Outputs the number in base 16, using |
225 | | upper-case letters for the digits above 9. Using the |
226 | | ``'#'`` option with this type adds the prefix ``"0X"`` |
227 | | to the output value. |
228 +---------+----------------------------------------------------------+
229 | none | The same as ``'d'``. |
230 +---------+----------------------------------------------------------+
231
232 Integer presentation types can also be used with character and Boolean values
233 with the only exception that ``'c'`` cannot be used with `bool`. Boolean values
234 are formatted using textual representation, either ``true`` or ``false``, if the
235 presentation type is not specified.
236
237 The available presentation types for floating-point values are:
238
239 +---------+----------------------------------------------------------+
240 | Type | Meaning |
241 +=========+==========================================================+
242 | ``'a'`` | Hexadecimal floating point format. Prints the number in |
243 | | base 16 with prefix ``"0x"`` and lower-case letters for |
244 | | digits above 9. Uses ``'p'`` to indicate the exponent. |
245 +---------+----------------------------------------------------------+
246 | ``'A'`` | Same as ``'a'`` except it uses upper-case letters for |
247 | | the prefix, digits above 9 and to indicate the exponent. |
248 +---------+----------------------------------------------------------+
249 | ``'e'`` | Exponent notation. Prints the number in scientific |
250 | | notation using the letter 'e' to indicate the exponent. |
251 +---------+----------------------------------------------------------+
252 | ``'E'`` | Exponent notation. Same as ``'e'`` except it uses an |
253 | | upper-case ``'E'`` as the separator character. |
254 +---------+----------------------------------------------------------+
255 | ``'f'`` | Fixed point. Displays the number as a fixed-point |
256 | | number. |
257 +---------+----------------------------------------------------------+
258 | ``'F'`` | Fixed point. Same as ``'f'``, but converts ``nan`` to |
259 | | ``NAN`` and ``inf`` to ``INF``. |
260 +---------+----------------------------------------------------------+
261 | ``'g'`` | General format. For a given precision ``p >= 1``, |
262 | | this rounds the number to ``p`` significant digits and |
263 | | then formats the result in either fixed-point format |
264 | | or in scientific notation, depending on its magnitude. |
265 | | |
266 | | A precision of ``0`` is treated as equivalent to a |
267 | | precision of ``1``. |
268 +---------+----------------------------------------------------------+
269 | ``'G'`` | General format. Same as ``'g'`` except switches to |
270 | | ``'E'`` if the number gets too large. The |
271 | | representations of infinity and NaN are uppercased, too. |
272 +---------+----------------------------------------------------------+
273 | none | Similar to ``'g'``, except that the default precision is |
274 | | as high as needed to represent the particular value. |
275 +---------+----------------------------------------------------------+
276
277 .. ifconfig:: False
278
279 +---------+----------------------------------------------------------+
280 | | The precise rules are as follows: suppose that the |
281 | | result formatted with presentation type ``'e'`` and |
282 | | precision ``p-1`` would have exponent ``exp``. Then |
283 | | if ``-4 <= exp < p``, the number is formatted |
284 | | with presentation type ``'f'`` and precision |
285 | | ``p-1-exp``. Otherwise, the number is formatted |
286 | | with presentation type ``'e'`` and precision ``p-1``. |
287 | | In both cases insignificant trailing zeros are removed |
288 | | from the significand, and the decimal point is also |
289 | | removed if there are no remaining digits following it. |
290 | | |
291 | | Positive and negative infinity, positive and negative |
292 | | zero, and nans, are formatted as ``inf``, ``-inf``, |
293 | | ``0``, ``-0`` and ``nan`` respectively, regardless of |
294 | | the precision. |
295 | | |
296 +---------+----------------------------------------------------------+
297
298 The available presentation types for pointers are:
299
300 +---------+----------------------------------------------------------+
301 | Type | Meaning |
302 +=========+==========================================================+
303 | ``'p'`` | Pointer format. This is the default type for |
304 | | pointers and may be omitted. |
305 +---------+----------------------------------------------------------+
306 | none | The same as ``'p'``. |
307 +---------+----------------------------------------------------------+
308
309 .. _chrono-specs:
310
311 Chrono Format Specifications
312 ============================
313
314 Format specifications for chrono duration and time point types as well as
315 ``std::tm`` have the following syntax:
316
317 .. productionlist:: sf
318 chrono_format_spec: [[`fill`]`align`][`width`]["." `precision`][`chrono_specs`]
319 chrono_specs: [`chrono_specs`] `conversion_spec` | `chrono_specs` `literal_char`
320 conversion_spec: "%" [`modifier`] `chrono_type`
321 literal_char: <a character other than '{', '}' or '%'>
322 modifier: "E" | "O"
323 chrono_type: "a" | "A" | "b" | "B" | "c" | "C" | "d" | "D" | "e" | "F" |
324 : "g" | "G" | "h" | "H" | "I" | "j" | "m" | "M" | "n" | "p" |
325 : "q" | "Q" | "r" | "R" | "S" | "t" | "T" | "u" | "U" | "V" |
326 : "w" | "W" | "x" | "X" | "y" | "Y" | "z" | "Z" | "%"
327
328 Literal chars are copied unchanged to the output. Precision is valid only for
329 ``std::chrono::duration`` types with a floating-point representation type.
330
331 The available presentation types (*chrono_type*) are:
332
333 +---------+--------------------------------------------------------------------+
334 | Type | Meaning |
335 +=========+====================================================================+
336 | ``'a'`` | The abbreviated weekday name, e.g. "Sat". If the value does not |
337 | | contain a valid weekday, an exception of type ``format_error`` is |
338 | | thrown. |
339 +---------+--------------------------------------------------------------------+
340 | ``'A'`` | The full weekday name, e.g. "Saturday". If the value does not |
341 | | contain a valid weekday, an exception of type ``format_error`` is |
342 | | thrown. |
343 +---------+--------------------------------------------------------------------+
344 | ``'b'`` | The abbreviated month name, e.g. "Nov". If the value does not |
345 | | contain a valid month, an exception of type ``format_error`` is |
346 | | thrown. |
347 +---------+--------------------------------------------------------------------+
348 | ``'B'`` | The full month name, e.g. "November". If the value does not |
349 | | contain a valid month, an exception of type ``format_error`` is |
350 | | thrown. |
351 +---------+--------------------------------------------------------------------+
352 | ``'c'`` | The date and time representation, e.g. "Sat Nov 12 22:04:00 1955". |
353 | | The modified command ``%Ec`` produces the locale's alternate date |
354 | | and time representation. |
355 +---------+--------------------------------------------------------------------+
356 | ``'C'`` | The year divided by 100 using floored division, e.g. "55". If the |
357 | | result is a single decimal digit, it is prefixed with 0. |
358 | | The modified command ``%EC`` produces the locale's alternative |
359 | | representation of the century. |
360 +---------+--------------------------------------------------------------------+
361 | ``'d'`` | The day of month as a decimal number. If the result is a single |
362 | | decimal digit, it is prefixed with 0. The modified command ``%Od`` |
363 | | produces the locale's alternative representation. |
364 +---------+--------------------------------------------------------------------+
365 | ``'D'`` | Equivalent to ``%m/%d/%y``, e.g. "11/12/55". |
366 +---------+--------------------------------------------------------------------+
367 | ``'e'`` | The day of month as a decimal number. If the result is a single |
368 | | decimal digit, it is prefixed with a space. The modified command |
369 | | ``%Oe`` produces the locale's alternative representation. |
370 +---------+--------------------------------------------------------------------+
371 | ``'F'`` | Equivalent to ``%Y-%m-%d``, e.g. "1955-11-12". |
372 +---------+--------------------------------------------------------------------+
373 | ``'g'`` | The last two decimal digits of the ISO week-based year. If the |
374 | | result is a single digit it is prefixed by 0. |
375 +---------+--------------------------------------------------------------------+
376 | ``'G'`` | The ISO week-based year as a decimal number. If the result is less |
377 | | than four digits it is left-padded with 0 to four digits. |
378 +---------+--------------------------------------------------------------------+
379 | ``'h'`` | Equivalent to ``%b``, e.g. "Nov". |
380 +---------+--------------------------------------------------------------------+
381 | ``'H'`` | The hour (24-hour clock) as a decimal number. If the result is a |
382 | | single digit, it is prefixed with 0. The modified command ``%OH`` |
383 | | produces the locale's alternative representation. |
384 +---------+--------------------------------------------------------------------+
385 | ``'I'`` | The hour (12-hour clock) as a decimal number. If the result is a |
386 | | single digit, it is prefixed with 0. The modified command ``%OI`` |
387 | | produces the locale's alternative representation. |
388 +---------+--------------------------------------------------------------------+
389 | ``'j'`` | If the type being formatted is a specialization of duration, the |
390 | | decimal number of days without padding. Otherwise, the day of the |
391 | | year as a decimal number. Jan 1 is 001. If the result is less than |
392 | | three digits, it is left-padded with 0 to three digits. |
393 +---------+--------------------------------------------------------------------+
394 | ``'m'`` | The month as a decimal number. Jan is 01. If the result is a |
395 | | single digit, it is prefixed with 0. The modified command ``%Om`` |
396 | | produces the locale's alternative representation. |
397 +---------+--------------------------------------------------------------------+
398 | ``'M'`` | The minute as a decimal number. If the result is a single digit, |
399 | | it is prefixed with 0. The modified command ``%OM`` produces the |
400 | | locale's alternative representation. |
401 +---------+--------------------------------------------------------------------+
402 | ``'n'`` | A new-line character. |
403 +---------+--------------------------------------------------------------------+
404 | ``'p'`` | The AM/PM designations associated with a 12-hour clock. |
405 +---------+--------------------------------------------------------------------+
406 | ``'q'`` | The duration's unit suffix. |
407 +---------+--------------------------------------------------------------------+
408 | ``'Q'`` | The duration's numeric value (as if extracted via ``.count()``). |
409 +---------+--------------------------------------------------------------------+
410 | ``'r'`` | The 12-hour clock time, e.g. "10:04:00 PM". |
411 +---------+--------------------------------------------------------------------+
412 | ``'R'`` | Equivalent to ``%H:%M``, e.g. "22:04". |
413 +---------+--------------------------------------------------------------------+
414 | ``'S'`` | Seconds as a decimal number. If the number of seconds is less than |
415 | | 10, the result is prefixed with 0. If the precision of the input |
416 | | cannot be exactly represented with seconds, then the format is a |
417 | | decimal floating-point number with a fixed format and a precision |
418 | | matching that of the precision of the input (or to a microseconds |
419 | | precision if the conversion to floating-point decimal seconds |
420 | | cannot be made within 18 fractional digits). The character for the |
421 | | decimal point is localized according to the locale. The modified |
422 | | command ``%OS`` produces the locale's alternative representation. |
423 +---------+--------------------------------------------------------------------+
424 | ``'t'`` | A horizontal-tab character. |
425 +---------+--------------------------------------------------------------------+
426 | ``'T'`` | Equivalent to ``%H:%M:%S``. |
427 +---------+--------------------------------------------------------------------+
428 | ``'u'`` | The ISO weekday as a decimal number (1-7), where Monday is 1. The |
429 | | modified command ``%Ou`` produces the locale's alternative |
430 | | representation. |
431 +---------+--------------------------------------------------------------------+
432 | ``'U'`` | The week number of the year as a decimal number. The first Sunday |
433 | | of the year is the first day of week 01. Days of the same year |
434 | | prior to that are in week 00. If the result is a single digit, it |
435 | | is prefixed with 0. The modified command ``%OU`` produces the |
436 | | locale's alternative representation. |
437 +---------+--------------------------------------------------------------------+
438 | ``'V'`` | The ISO week-based week number as a decimal number. If the result |
439 | | is a single digit, it is prefixed with 0. The modified command |
440 | | ``%OV`` produces the locale's alternative representation. |
441 +---------+--------------------------------------------------------------------+
442 | ``'w'`` | The weekday as a decimal number (0-6), where Sunday is 0. |
443 | | The modified command ``%Ow`` produces the locale's alternative |
444 | | representation. |
445 +---------+--------------------------------------------------------------------+
446 | ``'W'`` | The week number of the year as a decimal number. The first Monday |
447 | | of the year is the first day of week 01. Days of the same year |
448 | | prior to that are in week 00. If the result is a single digit, it |
449 | | is prefixed with 0. The modified command ``%OW`` produces the |
450 | | locale's alternative representation. |
451 +---------+--------------------------------------------------------------------+
452 | ``'x'`` | The date representation, e.g. "11/12/55". The modified command |
453 | | ``%Ex`` produces the locale's alternate date representation. |
454 +---------+--------------------------------------------------------------------+
455 | ``'X'`` | The time representation, e.g. "10:04:00". The modified command |
456 | | ``%EX`` produces the locale's alternate time representation. |
457 +---------+--------------------------------------------------------------------+
458 | ``'y'`` | The last two decimal digits of the year. If the result is a single |
459 | | digit it is prefixed by 0. The modified command ``%Oy`` produces |
460 | | the locale's alternative representation. The modified command |
461 | | ``%Ey`` produces the locale's alternative representation of offset |
462 | | from ``%EC`` (year only). |
463 +---------+--------------------------------------------------------------------+
464 | ``'Y'`` | The year as a decimal number. If the result is less than four |
465 | | digits it is left-padded with 0 to four digits. The modified |
466 | | command ``%EY`` produces the locale's alternative full year |
467 | | representation. |
468 +---------+--------------------------------------------------------------------+
469 | ``'z'`` | The offset from UTC in the ISO 8601:2004 format. For example -0430 |
470 | | refers to 4 hours 30 minutes behind UTC. If the offset is zero, |
471 | | +0000 is used. The modified commands ``%Ez`` and ``%Oz`` insert a |
472 | | ``:`` between the hours and minutes: -04:30. If the offset |
473 | | information is not available, an exception of type |
474 | | ``format_error`` is thrown. |
475 +---------+--------------------------------------------------------------------+
476 | ``'Z'`` | The time zone abbreviation. If the time zone abbreviation is not |
477 | | available, an exception of type ``format_error`` is thrown. |
478 +---------+--------------------------------------------------------------------+
479 | ``'%'`` | A % character. |
480 +---------+--------------------------------------------------------------------+
481
482 Specifiers that have a calendaric component such as ``'d'`` (the day of month)
483 are valid only for ``std::tm`` and time points but not durations.
484
485 .. range-specs:
486
487 Range Format Specifications
488 ===========================
489
490 Format specifications for range types have the following syntax:
491
492 .. productionlist:: sf
493 range_format_spec: [":" [`underlying_spec`]]
494
495 The `underlying_spec` is parsed based on the formatter of the range's
496 reference type.
497
498 By default, a range of characters or strings is printed escaped and quoted. But
499 if any `underlying_spec` is provided (even if it is empty), then the characters
500 or strings are printed according to the provided specification.
501
502 Examples::
503
504 fmt::format("{}", std::vector{10, 20, 30});
505 // Result: [10, 20, 30]
506 fmt::format("{::#x}", std::vector{10, 20, 30});
507 // Result: [0xa, 0x14, 0x1e]
508 fmt::format("{}", vector{'h', 'e', 'l', 'l', 'o'});
509 // Result: ['h', 'e', 'l', 'l', 'o']
510 fmt::format("{::}", vector{'h', 'e', 'l', 'l', 'o'});
511 // Result: [h, e, l, l, o]
512 fmt::format("{::d}", vector{'h', 'e', 'l', 'l', 'o'});
513 // Result: [104, 101, 108, 108, 111]
514
515 .. _formatexamples:
516
517 Format Examples
518 ===============
519
520 This section contains examples of the format syntax and comparison with
521 the printf formatting.
522
523 In most of the cases the syntax is similar to the printf formatting, with the
524 addition of the ``{}`` and with ``:`` used instead of ``%``.
525 For example, ``"%03.2f"`` can be translated to ``"{:03.2f}"``.
526
527 The new format syntax also supports new and different options, shown in the
528 following examples.
529
530 Accessing arguments by position::
531
532 fmt::format("{0}, {1}, {2}", 'a', 'b', 'c');
533 // Result: "a, b, c"
534 fmt::format("{}, {}, {}", 'a', 'b', 'c');
535 // Result: "a, b, c"
536 fmt::format("{2}, {1}, {0}", 'a', 'b', 'c');
537 // Result: "c, b, a"
538 fmt::format("{0}{1}{0}", "abra", "cad"); // arguments' indices can be repeated
539 // Result: "abracadabra"
540
541 Aligning the text and specifying a width::
542
543 fmt::format("{:<30}", "left aligned");
544 // Result: "left aligned "
545 fmt::format("{:>30}", "right aligned");
546 // Result: " right aligned"
547 fmt::format("{:^30}", "centered");
548 // Result: " centered "
549 fmt::format("{:*^30}", "centered"); // use '*' as a fill char
550 // Result: "***********centered***********"
551
552 Dynamic width::
553
554 fmt::format("{:<{}}", "left aligned", 30);
555 // Result: "left aligned "
556
557 Dynamic precision::
558
559 fmt::format("{:.{}f}", 3.14, 1);
560 // Result: "3.1"
561
562 Replacing ``%+f``, ``%-f``, and ``% f`` and specifying a sign::
563
564 fmt::format("{:+f}; {:+f}", 3.14, -3.14); // show it always
565 // Result: "+3.140000; -3.140000"
566 fmt::format("{: f}; {: f}", 3.14, -3.14); // show a space for positive numbers
567 // Result: " 3.140000; -3.140000"
568 fmt::format("{:-f}; {:-f}", 3.14, -3.14); // show only the minus -- same as '{:f}; {:f}'
569 // Result: "3.140000; -3.140000"
570
571 Replacing ``%x`` and ``%o`` and converting the value to different bases::
572
573 fmt::format("int: {0:d}; hex: {0:x}; oct: {0:o}; bin: {0:b}", 42);
574 // Result: "int: 42; hex: 2a; oct: 52; bin: 101010"
575 // with 0x or 0 or 0b as prefix:
576 fmt::format("int: {0:d}; hex: {0:#x}; oct: {0:#o}; bin: {0:#b}", 42);
577 // Result: "int: 42; hex: 0x2a; oct: 052; bin: 0b101010"
578
579 Padded hex byte with prefix and always prints both hex characters::
580
581 fmt::format("{:#04x}", 0);
582 // Result: "0x00"
583
584 Box drawing using Unicode fill::
585
586 fmt::print(
587 "┌{0:─^{2}}┐\n"
588 "│{1: ^{2}}│\n"
589 "└{0:─^{2}}┘\n", "", "Hello, world!", 20);
590
591 prints::
592
593 ┌────────────────────┐
594 │ Hello, world! │
595 └────────────────────┘
596
597 Using type-specific formatting::
598
599 #include <fmt/chrono.h>
600
601 auto t = tm();
602 t.tm_year = 2010 - 1900;
603 t.tm_mon = 7;
604 t.tm_mday = 4;
605 t.tm_hour = 12;
606 t.tm_min = 15;
607 t.tm_sec = 58;
608 fmt::print("{:%Y-%m-%d %H:%M:%S}", t);
609 // Prints: 2010-08-04 12:15:58
610
611 Using the comma as a thousands separator::
612
613 #include <fmt/format.h>
614
615 auto s = fmt::format(std::locale("en_US.UTF-8"), "{:L}", 1234567890);
616 // s == "1,234,567,890"
617
618 .. ifconfig:: False
619
620 Nesting arguments and more complex examples::
621
622 >>> for align, text in zip('<^>', ['left', 'center', 'right']):
623 ... '{0:{fill}{align}16}") << text, fill=align, align=align)
624 ...
625 'left<<<<<<<<<<<<'
626 '^^^^^center^^^^^'
627 '>>>>>>>>>>>right'
628 >>>
629 >>> octets = [192, 168, 0, 1]
630 Format("{:02X}{:02X}{:02X}{:02X}") << *octets)
631 'C0A80001'
632 >>> int(_, 16)
633 3232235521
634 >>>
635 >>> width = 5
636 >>> for num in range(5,12):
637 ... for base in 'dXob':
638 ... print('{0:{width}{base}}") << num, base=base, width=width), end=' ')
639 ... print()
640 ...
641 5 5 5 101
642 6 6 6 110
643 7 7 7 111
644 8 8 10 1000
645 9 9 11 1001
646 10 A 12 1010
647 11 B 13 1011