Mercurial > minori
diff dep/fmt/doc/syntax.rst @ 343:1faa72660932
*: 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 |
| parents | |
| children |
line wrap: on
line diff
--- /dev/null Thu Jan 01 00:00:00 1970 +0000 +++ b/dep/fmt/doc/syntax.rst Thu Jun 20 05:56:06 2024 -0400 @@ -0,0 +1,647 @@ +.. _syntax: + +******************** +Format String Syntax +******************** + +Formatting functions such as :ref:`fmt::format() <format>` and +:ref:`fmt::print() <print>` use the same format string syntax described in this +section. + +Format strings contain "replacement fields" surrounded by curly braces ``{}``. +Anything that is not contained in braces is considered literal text, which is +copied unchanged to the output. If you need to include a brace character in the +literal text, it can be escaped by doubling: ``{{`` and ``}}``. + +The grammar for a replacement field is as follows: + +.. productionlist:: sf + replacement_field: "{" [`arg_id`] [":" (`format_spec` | `chrono_format_spec`)] "}" + arg_id: `integer` | `identifier` + integer: `digit`+ + digit: "0"..."9" + identifier: `id_start` `id_continue`* + id_start: "a"..."z" | "A"..."Z" | "_" + id_continue: `id_start` | `digit` + +In less formal terms, the replacement field can start with an *arg_id* +that specifies the argument whose value is to be formatted and inserted into +the output instead of the replacement field. +The *arg_id* is optionally followed by a *format_spec*, which is preceded by a +colon ``':'``. These specify a non-default format for the replacement value. + +See also the :ref:`formatspec` section. + +If the numerical arg_ids in a format string are 0, 1, 2, ... in sequence, +they can all be omitted (not just some) and the numbers 0, 1, 2, ... will be +automatically inserted in that order. + +Named arguments can be referred to by their names or indices. + +Some simple format string examples:: + + "First, thou shalt count to {0}" // References the first argument + "Bring me a {}" // Implicitly references the first argument + "From {} to {}" // Same as "From {0} to {1}" + +The *format_spec* field contains a specification of how the value should be +presented, including such details as field width, alignment, padding, decimal +precision and so on. Each value type can define its own "formatting +mini-language" or interpretation of the *format_spec*. + +Most built-in types support a common formatting mini-language, which is +described in the next section. + +A *format_spec* field can also include nested replacement fields in certain +positions within it. These nested replacement fields can contain only an +argument id; format specifications are not allowed. This allows the formatting +of a value to be dynamically specified. + +See the :ref:`formatexamples` section for some examples. + +.. _formatspec: + +Format Specification Mini-Language +================================== + +"Format specifications" are used within replacement fields contained within a +format string to define how individual values are presented (see +:ref:`syntax`). Each formattable type may define how the format +specification is to be interpreted. + +Most built-in types implement the following options for format specifications, +although some of the formatting options are only supported by the numeric types. + +The general form of a *standard format specifier* is: + +.. productionlist:: sf + format_spec: [[`fill`]`align`][`sign`]["#"]["0"][`width`]["." `precision`]["L"][`type`] + fill: <a character other than '{' or '}'> + align: "<" | ">" | "^" + sign: "+" | "-" | " " + width: `integer` | "{" [`arg_id`] "}" + precision: `integer` | "{" [`arg_id`] "}" + type: "a" | "A" | "b" | "B" | "c" | "d" | "e" | "E" | "f" | "F" | "g" | "G" | + : "o" | "p" | "s" | "x" | "X" | "?" + +The *fill* character can be any Unicode code point other than ``'{'`` or +``'}'``. The presence of a fill character is signaled by the character following +it, which must be one of the alignment options. If the second character of +*format_spec* is not a valid alignment option, then it is assumed that both the +fill character and the alignment option are absent. + +The meaning of the various alignment options is as follows: + ++---------+----------------------------------------------------------+ +| Option | Meaning | ++=========+==========================================================+ +| ``'<'`` | Forces the field to be left-aligned within the available | +| | space (this is the default for most objects). | ++---------+----------------------------------------------------------+ +| ``'>'`` | Forces the field to be right-aligned within the | +| | available space (this is the default for numbers). | ++---------+----------------------------------------------------------+ +| ``'^'`` | Forces the field to be centered within the available | +| | space. | ++---------+----------------------------------------------------------+ + +Note that unless a minimum field width is defined, the field width will always +be the same size as the data to fill it, so that the alignment option has no +meaning in this case. + +The *sign* option is only valid for floating point and signed integer types, +and can be one of the following: + ++---------+------------------------------------------------------------+ +| Option | Meaning | ++=========+============================================================+ +| ``'+'`` | indicates that a sign should be used for both | +| | nonnegative as well as negative numbers. | ++---------+------------------------------------------------------------+ +| ``'-'`` | indicates that a sign should be used only for negative | +| | numbers (this is the default behavior). | ++---------+------------------------------------------------------------+ +| space | indicates that a leading space should be used on | +| | nonnegative numbers, and a minus sign on negative numbers. | ++---------+------------------------------------------------------------+ + +The ``'#'`` option causes the "alternate form" to be used for the +conversion. The alternate form is defined differently for different +types. This option is only valid for integer and floating-point types. +For integers, when binary, octal, or hexadecimal output is used, this +option adds the prefix respective ``"0b"`` (``"0B"``), ``"0"``, or +``"0x"`` (``"0X"``) to the output value. Whether the prefix is +lower-case or upper-case is determined by the case of the type +specifier, for example, the prefix ``"0x"`` is used for the type ``'x'`` +and ``"0X"`` is used for ``'X'``. For floating-point numbers the +alternate form causes the result of the conversion to always contain a +decimal-point character, even if no digits follow it. Normally, a +decimal-point character appears in the result of these conversions +only if a digit follows it. In addition, for ``'g'`` and ``'G'`` +conversions, trailing zeros are not removed from the result. + +.. ifconfig:: False + + The ``','`` option signals the use of a comma for a thousands separator. + For a locale aware separator, use the ``'L'`` integer presentation type + instead. + +*width* is a decimal integer defining the minimum field width. If not +specified, then the field width will be determined by the content. + +Preceding the *width* field by a zero (``'0'``) character enables sign-aware +zero-padding for numeric types. It forces the padding to be placed after the +sign or base (if any) but before the digits. This is used for printing fields in +the form '+000000120'. This option is only valid for numeric types and it has no +effect on formatting of infinity and NaN. + +The *precision* is a decimal number indicating how many digits should be +displayed after the decimal point for a floating-point value formatted with +``'f'`` and ``'F'``, or before and after the decimal point for a floating-point +value formatted with ``'g'`` or ``'G'``. For non-number types the field +indicates the maximum field size - in other words, how many characters will be +used from the field content. The *precision* is not allowed for integer, +character, Boolean, and pointer values. Note that a C string must be +null-terminated even if precision is specified. + +The ``'L'`` option uses the current locale setting to insert the appropriate +number separator characters. This option is only valid for numeric types. + +Finally, the *type* determines how the data should be presented. + +The available string presentation types are: + ++---------+----------------------------------------------------------+ +| Type | Meaning | ++=========+==========================================================+ +| ``'s'`` | String format. This is the default type for strings and | +| | may be omitted. | ++---------+----------------------------------------------------------+ +| ``'?'`` | Debug format. The string is quoted and special | +| | characters escaped. | ++---------+----------------------------------------------------------+ +| none | The same as ``'s'``. | ++---------+----------------------------------------------------------+ + +The available character presentation types are: + ++---------+----------------------------------------------------------+ +| Type | Meaning | ++=========+==========================================================+ +| ``'c'`` | Character format. This is the default type for | +| | characters and may be omitted. | ++---------+----------------------------------------------------------+ +| ``'?'`` | Debug format. The character is quoted and special | +| | characters escaped. | ++---------+----------------------------------------------------------+ +| none | The same as ``'c'``. | ++---------+----------------------------------------------------------+ + +The available integer presentation types are: + ++---------+----------------------------------------------------------+ +| Type | Meaning | ++=========+==========================================================+ +| ``'b'`` | Binary format. Outputs the number in base 2. Using the | +| | ``'#'`` option with this type adds the prefix ``"0b"`` | +| | to the output value. | ++---------+----------------------------------------------------------+ +| ``'B'`` | Binary format. Outputs the number in base 2. Using the | +| | ``'#'`` option with this type adds the prefix ``"0B"`` | +| | to the output value. | ++---------+----------------------------------------------------------+ +| ``'c'`` | Character format. Outputs the number as a character. | ++---------+----------------------------------------------------------+ +| ``'d'`` | Decimal integer. Outputs the number in base 10. | ++---------+----------------------------------------------------------+ +| ``'o'`` | Octal format. Outputs the number in base 8. | ++---------+----------------------------------------------------------+ +| ``'x'`` | Hex format. Outputs the number in base 16, using | +| | lower-case letters for the digits above 9. Using the | +| | ``'#'`` option with this type adds the prefix ``"0x"`` | +| | to the output value. | ++---------+----------------------------------------------------------+ +| ``'X'`` | Hex format. Outputs the number in base 16, using | +| | upper-case letters for the digits above 9. Using the | +| | ``'#'`` option with this type adds the prefix ``"0X"`` | +| | to the output value. | ++---------+----------------------------------------------------------+ +| none | The same as ``'d'``. | ++---------+----------------------------------------------------------+ + +Integer presentation types can also be used with character and Boolean values +with the only exception that ``'c'`` cannot be used with `bool`. Boolean values +are formatted using textual representation, either ``true`` or ``false``, if the +presentation type is not specified. + +The available presentation types for floating-point values are: + ++---------+----------------------------------------------------------+ +| Type | Meaning | ++=========+==========================================================+ +| ``'a'`` | Hexadecimal floating point format. Prints the number in | +| | base 16 with prefix ``"0x"`` and lower-case letters for | +| | digits above 9. Uses ``'p'`` to indicate the exponent. | ++---------+----------------------------------------------------------+ +| ``'A'`` | Same as ``'a'`` except it uses upper-case letters for | +| | the prefix, digits above 9 and to indicate the exponent. | ++---------+----------------------------------------------------------+ +| ``'e'`` | Exponent notation. Prints the number in scientific | +| | notation using the letter 'e' to indicate the exponent. | ++---------+----------------------------------------------------------+ +| ``'E'`` | Exponent notation. Same as ``'e'`` except it uses an | +| | upper-case ``'E'`` as the separator character. | ++---------+----------------------------------------------------------+ +| ``'f'`` | Fixed point. Displays the number as a fixed-point | +| | number. | ++---------+----------------------------------------------------------+ +| ``'F'`` | Fixed point. Same as ``'f'``, but converts ``nan`` to | +| | ``NAN`` and ``inf`` to ``INF``. | ++---------+----------------------------------------------------------+ +| ``'g'`` | General format. For a given precision ``p >= 1``, | +| | this rounds the number to ``p`` significant digits and | +| | then formats the result in either fixed-point format | +| | or in scientific notation, depending on its magnitude. | +| | | +| | A precision of ``0`` is treated as equivalent to a | +| | precision of ``1``. | ++---------+----------------------------------------------------------+ +| ``'G'`` | General format. Same as ``'g'`` except switches to | +| | ``'E'`` if the number gets too large. The | +| | representations of infinity and NaN are uppercased, too. | ++---------+----------------------------------------------------------+ +| none | Similar to ``'g'``, except that the default precision is | +| | as high as needed to represent the particular value. | ++---------+----------------------------------------------------------+ + +.. ifconfig:: False + + +---------+----------------------------------------------------------+ + | | The precise rules are as follows: suppose that the | + | | result formatted with presentation type ``'e'`` and | + | | precision ``p-1`` would have exponent ``exp``. Then | + | | if ``-4 <= exp < p``, the number is formatted | + | | with presentation type ``'f'`` and precision | + | | ``p-1-exp``. Otherwise, the number is formatted | + | | with presentation type ``'e'`` and precision ``p-1``. | + | | In both cases insignificant trailing zeros are removed | + | | from the significand, and the decimal point is also | + | | removed if there are no remaining digits following it. | + | | | + | | Positive and negative infinity, positive and negative | + | | zero, and nans, are formatted as ``inf``, ``-inf``, | + | | ``0``, ``-0`` and ``nan`` respectively, regardless of | + | | the precision. | + | | | + +---------+----------------------------------------------------------+ + +The available presentation types for pointers are: + ++---------+----------------------------------------------------------+ +| Type | Meaning | ++=========+==========================================================+ +| ``'p'`` | Pointer format. This is the default type for | +| | pointers and may be omitted. | ++---------+----------------------------------------------------------+ +| none | The same as ``'p'``. | ++---------+----------------------------------------------------------+ + +.. _chrono-specs: + +Chrono Format Specifications +============================ + +Format specifications for chrono duration and time point types as well as +``std::tm`` have the following syntax: + +.. productionlist:: sf + chrono_format_spec: [[`fill`]`align`][`width`]["." `precision`][`chrono_specs`] + chrono_specs: [`chrono_specs`] `conversion_spec` | `chrono_specs` `literal_char` + conversion_spec: "%" [`modifier`] `chrono_type` + literal_char: <a character other than '{', '}' or '%'> + modifier: "E" | "O" + chrono_type: "a" | "A" | "b" | "B" | "c" | "C" | "d" | "D" | "e" | "F" | + : "g" | "G" | "h" | "H" | "I" | "j" | "m" | "M" | "n" | "p" | + : "q" | "Q" | "r" | "R" | "S" | "t" | "T" | "u" | "U" | "V" | + : "w" | "W" | "x" | "X" | "y" | "Y" | "z" | "Z" | "%" + +Literal chars are copied unchanged to the output. Precision is valid only for +``std::chrono::duration`` types with a floating-point representation type. + +The available presentation types (*chrono_type*) are: + ++---------+--------------------------------------------------------------------+ +| Type | Meaning | ++=========+====================================================================+ +| ``'a'`` | The abbreviated weekday name, e.g. "Sat". If the value does not | +| | contain a valid weekday, an exception of type ``format_error`` is | +| | thrown. | ++---------+--------------------------------------------------------------------+ +| ``'A'`` | The full weekday name, e.g. "Saturday". If the value does not | +| | contain a valid weekday, an exception of type ``format_error`` is | +| | thrown. | ++---------+--------------------------------------------------------------------+ +| ``'b'`` | The abbreviated month name, e.g. "Nov". If the value does not | +| | contain a valid month, an exception of type ``format_error`` is | +| | thrown. | ++---------+--------------------------------------------------------------------+ +| ``'B'`` | The full month name, e.g. "November". If the value does not | +| | contain a valid month, an exception of type ``format_error`` is | +| | thrown. | ++---------+--------------------------------------------------------------------+ +| ``'c'`` | The date and time representation, e.g. "Sat Nov 12 22:04:00 1955". | +| | The modified command ``%Ec`` produces the locale's alternate date | +| | and time representation. | ++---------+--------------------------------------------------------------------+ +| ``'C'`` | The year divided by 100 using floored division, e.g. "55". If the | +| | result is a single decimal digit, it is prefixed with 0. | +| | The modified command ``%EC`` produces the locale's alternative | +| | representation of the century. | ++---------+--------------------------------------------------------------------+ +| ``'d'`` | The day of month as a decimal number. If the result is a single | +| | decimal digit, it is prefixed with 0. The modified command ``%Od`` | +| | produces the locale's alternative representation. | ++---------+--------------------------------------------------------------------+ +| ``'D'`` | Equivalent to ``%m/%d/%y``, e.g. "11/12/55". | ++---------+--------------------------------------------------------------------+ +| ``'e'`` | The day of month as a decimal number. If the result is a single | +| | decimal digit, it is prefixed with a space. The modified command | +| | ``%Oe`` produces the locale's alternative representation. | ++---------+--------------------------------------------------------------------+ +| ``'F'`` | Equivalent to ``%Y-%m-%d``, e.g. "1955-11-12". | ++---------+--------------------------------------------------------------------+ +| ``'g'`` | The last two decimal digits of the ISO week-based year. If the | +| | result is a single digit it is prefixed by 0. | ++---------+--------------------------------------------------------------------+ +| ``'G'`` | The ISO week-based year as a decimal number. If the result is less | +| | than four digits it is left-padded with 0 to four digits. | ++---------+--------------------------------------------------------------------+ +| ``'h'`` | Equivalent to ``%b``, e.g. "Nov". | ++---------+--------------------------------------------------------------------+ +| ``'H'`` | The hour (24-hour clock) as a decimal number. If the result is a | +| | single digit, it is prefixed with 0. The modified command ``%OH`` | +| | produces the locale's alternative representation. | ++---------+--------------------------------------------------------------------+ +| ``'I'`` | The hour (12-hour clock) as a decimal number. If the result is a | +| | single digit, it is prefixed with 0. The modified command ``%OI`` | +| | produces the locale's alternative representation. | ++---------+--------------------------------------------------------------------+ +| ``'j'`` | If the type being formatted is a specialization of duration, the | +| | decimal number of days without padding. Otherwise, the day of the | +| | year as a decimal number. Jan 1 is 001. If the result is less than | +| | three digits, it is left-padded with 0 to three digits. | ++---------+--------------------------------------------------------------------+ +| ``'m'`` | The month as a decimal number. Jan is 01. If the result is a | +| | single digit, it is prefixed with 0. The modified command ``%Om`` | +| | produces the locale's alternative representation. | ++---------+--------------------------------------------------------------------+ +| ``'M'`` | The minute as a decimal number. If the result is a single digit, | +| | it is prefixed with 0. The modified command ``%OM`` produces the | +| | locale's alternative representation. | ++---------+--------------------------------------------------------------------+ +| ``'n'`` | A new-line character. | ++---------+--------------------------------------------------------------------+ +| ``'p'`` | The AM/PM designations associated with a 12-hour clock. | ++---------+--------------------------------------------------------------------+ +| ``'q'`` | The duration's unit suffix. | ++---------+--------------------------------------------------------------------+ +| ``'Q'`` | The duration's numeric value (as if extracted via ``.count()``). | ++---------+--------------------------------------------------------------------+ +| ``'r'`` | The 12-hour clock time, e.g. "10:04:00 PM". | ++---------+--------------------------------------------------------------------+ +| ``'R'`` | Equivalent to ``%H:%M``, e.g. "22:04". | ++---------+--------------------------------------------------------------------+ +| ``'S'`` | Seconds as a decimal number. If the number of seconds is less than | +| | 10, the result is prefixed with 0. If the precision of the input | +| | cannot be exactly represented with seconds, then the format is a | +| | decimal floating-point number with a fixed format and a precision | +| | matching that of the precision of the input (or to a microseconds | +| | precision if the conversion to floating-point decimal seconds | +| | cannot be made within 18 fractional digits). The character for the | +| | decimal point is localized according to the locale. The modified | +| | command ``%OS`` produces the locale's alternative representation. | ++---------+--------------------------------------------------------------------+ +| ``'t'`` | A horizontal-tab character. | ++---------+--------------------------------------------------------------------+ +| ``'T'`` | Equivalent to ``%H:%M:%S``. | ++---------+--------------------------------------------------------------------+ +| ``'u'`` | The ISO weekday as a decimal number (1-7), where Monday is 1. The | +| | modified command ``%Ou`` produces the locale's alternative | +| | representation. | ++---------+--------------------------------------------------------------------+ +| ``'U'`` | The week number of the year as a decimal number. The first Sunday | +| | of the year is the first day of week 01. Days of the same year | +| | prior to that are in week 00. If the result is a single digit, it | +| | is prefixed with 0. The modified command ``%OU`` produces the | +| | locale's alternative representation. | ++---------+--------------------------------------------------------------------+ +| ``'V'`` | The ISO week-based week number as a decimal number. If the result | +| | is a single digit, it is prefixed with 0. The modified command | +| | ``%OV`` produces the locale's alternative representation. | ++---------+--------------------------------------------------------------------+ +| ``'w'`` | The weekday as a decimal number (0-6), where Sunday is 0. | +| | The modified command ``%Ow`` produces the locale's alternative | +| | representation. | ++---------+--------------------------------------------------------------------+ +| ``'W'`` | The week number of the year as a decimal number. The first Monday | +| | of the year is the first day of week 01. Days of the same year | +| | prior to that are in week 00. If the result is a single digit, it | +| | is prefixed with 0. The modified command ``%OW`` produces the | +| | locale's alternative representation. | ++---------+--------------------------------------------------------------------+ +| ``'x'`` | The date representation, e.g. "11/12/55". The modified command | +| | ``%Ex`` produces the locale's alternate date representation. | ++---------+--------------------------------------------------------------------+ +| ``'X'`` | The time representation, e.g. "10:04:00". The modified command | +| | ``%EX`` produces the locale's alternate time representation. | ++---------+--------------------------------------------------------------------+ +| ``'y'`` | The last two decimal digits of the year. If the result is a single | +| | digit it is prefixed by 0. The modified command ``%Oy`` produces | +| | the locale's alternative representation. The modified command | +| | ``%Ey`` produces the locale's alternative representation of offset | +| | from ``%EC`` (year only). | ++---------+--------------------------------------------------------------------+ +| ``'Y'`` | The year as a decimal number. If the result is less than four | +| | digits it is left-padded with 0 to four digits. The modified | +| | command ``%EY`` produces the locale's alternative full year | +| | representation. | ++---------+--------------------------------------------------------------------+ +| ``'z'`` | The offset from UTC in the ISO 8601:2004 format. For example -0430 | +| | refers to 4 hours 30 minutes behind UTC. If the offset is zero, | +| | +0000 is used. The modified commands ``%Ez`` and ``%Oz`` insert a | +| | ``:`` between the hours and minutes: -04:30. If the offset | +| | information is not available, an exception of type | +| | ``format_error`` is thrown. | ++---------+--------------------------------------------------------------------+ +| ``'Z'`` | The time zone abbreviation. If the time zone abbreviation is not | +| | available, an exception of type ``format_error`` is thrown. | ++---------+--------------------------------------------------------------------+ +| ``'%'`` | A % character. | ++---------+--------------------------------------------------------------------+ + +Specifiers that have a calendaric component such as ``'d'`` (the day of month) +are valid only for ``std::tm`` and time points but not durations. + +.. range-specs: + +Range Format Specifications +=========================== + +Format specifications for range types have the following syntax: + +.. productionlist:: sf + range_format_spec: [":" [`underlying_spec`]] + +The `underlying_spec` is parsed based on the formatter of the range's +reference type. + +By default, a range of characters or strings is printed escaped and quoted. But +if any `underlying_spec` is provided (even if it is empty), then the characters +or strings are printed according to the provided specification. + +Examples:: + + fmt::format("{}", std::vector{10, 20, 30}); + // Result: [10, 20, 30] + fmt::format("{::#x}", std::vector{10, 20, 30}); + // Result: [0xa, 0x14, 0x1e] + fmt::format("{}", vector{'h', 'e', 'l', 'l', 'o'}); + // Result: ['h', 'e', 'l', 'l', 'o'] + fmt::format("{::}", vector{'h', 'e', 'l', 'l', 'o'}); + // Result: [h, e, l, l, o] + fmt::format("{::d}", vector{'h', 'e', 'l', 'l', 'o'}); + // Result: [104, 101, 108, 108, 111] + +.. _formatexamples: + +Format Examples +=============== + +This section contains examples of the format syntax and comparison with +the printf formatting. + +In most of the cases the syntax is similar to the printf formatting, with the +addition of the ``{}`` and with ``:`` used instead of ``%``. +For example, ``"%03.2f"`` can be translated to ``"{:03.2f}"``. + +The new format syntax also supports new and different options, shown in the +following examples. + +Accessing arguments by position:: + + fmt::format("{0}, {1}, {2}", 'a', 'b', 'c'); + // Result: "a, b, c" + fmt::format("{}, {}, {}", 'a', 'b', 'c'); + // Result: "a, b, c" + fmt::format("{2}, {1}, {0}", 'a', 'b', 'c'); + // Result: "c, b, a" + fmt::format("{0}{1}{0}", "abra", "cad"); // arguments' indices can be repeated + // Result: "abracadabra" + +Aligning the text and specifying a width:: + + fmt::format("{:<30}", "left aligned"); + // Result: "left aligned " + fmt::format("{:>30}", "right aligned"); + // Result: " right aligned" + fmt::format("{:^30}", "centered"); + // Result: " centered " + fmt::format("{:*^30}", "centered"); // use '*' as a fill char + // Result: "***********centered***********" + +Dynamic width:: + + fmt::format("{:<{}}", "left aligned", 30); + // Result: "left aligned " + +Dynamic precision:: + + fmt::format("{:.{}f}", 3.14, 1); + // Result: "3.1" + +Replacing ``%+f``, ``%-f``, and ``% f`` and specifying a sign:: + + fmt::format("{:+f}; {:+f}", 3.14, -3.14); // show it always + // Result: "+3.140000; -3.140000" + fmt::format("{: f}; {: f}", 3.14, -3.14); // show a space for positive numbers + // Result: " 3.140000; -3.140000" + fmt::format("{:-f}; {:-f}", 3.14, -3.14); // show only the minus -- same as '{:f}; {:f}' + // Result: "3.140000; -3.140000" + +Replacing ``%x`` and ``%o`` and converting the value to different bases:: + + fmt::format("int: {0:d}; hex: {0:x}; oct: {0:o}; bin: {0:b}", 42); + // Result: "int: 42; hex: 2a; oct: 52; bin: 101010" + // with 0x or 0 or 0b as prefix: + fmt::format("int: {0:d}; hex: {0:#x}; oct: {0:#o}; bin: {0:#b}", 42); + // Result: "int: 42; hex: 0x2a; oct: 052; bin: 0b101010" + +Padded hex byte with prefix and always prints both hex characters:: + + fmt::format("{:#04x}", 0); + // Result: "0x00" + +Box drawing using Unicode fill:: + + fmt::print( + "┌{0:─^{2}}┐\n" + "│{1: ^{2}}│\n" + "└{0:─^{2}}┘\n", "", "Hello, world!", 20); + +prints:: + + ┌────────────────────┐ + │ Hello, world! │ + └────────────────────┘ + +Using type-specific formatting:: + + #include <fmt/chrono.h> + + auto t = tm(); + t.tm_year = 2010 - 1900; + t.tm_mon = 7; + t.tm_mday = 4; + t.tm_hour = 12; + t.tm_min = 15; + t.tm_sec = 58; + fmt::print("{:%Y-%m-%d %H:%M:%S}", t); + // Prints: 2010-08-04 12:15:58 + +Using the comma as a thousands separator:: + + #include <fmt/format.h> + + auto s = fmt::format(std::locale("en_US.UTF-8"), "{:L}", 1234567890); + // s == "1,234,567,890" + +.. ifconfig:: False + + Nesting arguments and more complex examples:: + + >>> for align, text in zip('<^>', ['left', 'center', 'right']): + ... '{0:{fill}{align}16}") << text, fill=align, align=align) + ... + 'left<<<<<<<<<<<<' + '^^^^^center^^^^^' + '>>>>>>>>>>>right' + >>> + >>> octets = [192, 168, 0, 1] + Format("{:02X}{:02X}{:02X}{:02X}") << *octets) + 'C0A80001' + >>> int(_, 16) + 3232235521 + >>> + >>> width = 5 + >>> for num in range(5,12): + ... for base in 'dXob': + ... print('{0:{width}{base}}") << num, base=base, width=width), end=' ') + ... print() + ... + 5 5 5 101 + 6 6 6 110 + 7 7 7 111 + 8 8 10 1000 + 9 9 11 1001 + 10 A 12 1010 + 11 B 13 1011