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@ -1,14 +1,15 @@
# Format String Syntax
Formatting functions such as [`fmt::format`](api.md#format) and [`fmt::print`](
api.md#print) use the same format string syntax described in this section.
The formatting functions in this library — most notably
[`fmt::format`](api.md#format) and [`fmt::print`](api.md#print) — accept
format strings written in the syntax described here.
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 `}}`.
A format string is plain text with embedded *replacement fields* delimited by
the braces `{` and `}`. Characters outside of any replacement field are
copied to the output unchanged. To emit a literal brace, double it: `{{`
yields a single `{` in the output, and `}}` yields a single `}`.
The grammar for a replacement field is as follows:
A replacement field is described by the grammar below.
<a id="replacement-field"></a>
<pre><code class="language-json"
@ -22,55 +23,43 @@ id_start ::= "a"..."z" | "A"..."Z" | "_"
id_continue ::= id_start | digit</code>
</pre>
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.
An *arg_id* selects which argument to format. It may be a non-negative
integer (positional reference) or an identifier matching the name of an
argument passed via [`fmt::arg`](api.md#arg) (named reference). When *arg_id*
is omitted, arguments are consumed in left-to-right order; this *automatic*
indexing must be used uniformly throughout the format string — mixing
automatic and explicit numeric ids is a compile-time error (or a
`format_error` at runtime).
See also the [Format Specification
Mini-Language](#format-specification-mini-language) section.
A *format_spec*, introduced by `:`, describes how the value should be
rendered. Its grammar is type-dependent; the form used by the standard
built-in types is documented in the next 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:
For example:
```c++
"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}"
fmt::format("hello, {}", "world");
// Result: "hello, world"
fmt::format("{1}, {0}!", "world", "hello");
// Result: "hello, world!"
fmt::format("{greeting}, {name}!",
fmt::arg("greeting", "hi"), fmt::arg("name", "fmt"));
// Result: "hi, fmt!"
```
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*.
A *width* or *precision* inside a *format_spec* may itself be written as a
nested replacement field — `{}` or `{arg_id}` — in which case it takes its
value from an integer argument at runtime. Nested fields accept only an
*arg_id*; they cannot themselves contain a *format_spec*.
Most built-in types support a common formatting mini-language, which is
described in the next section.
## Standard Format Specification
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 [Format Examples](#format-examples) section for some examples.
## Format Specification Mini-Language
"Format specifications" are used within replacement fields contained within a
format string to define how individual values are presented. 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:
The grammar below describes the *format_spec* shared by the standard built-in
types — integers, floating-point values, characters, strings, booleans, and
pointers — as well as by any user-defined type whose `formatter` reuses
fmt's parser.
<a id="format-spec"></a>
<pre><code class="language-json"
@ -86,313 +75,212 @@ type ::= "a" | "A" | "b" | "B" | "c" | "d" | "e" | "E" | "f" | "F" |
"g" | "G" | "o" | "p" | "s" | "x" | "X" | "?"</code>
</pre>
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.
Whether a particular option is meaningful depends on the value being
formatted; options that do not apply to a value's type are diagnosed at
compile time when possible and otherwise raise a `format_error`.
The meaning of the various alignment options is as follows:
### Fill and alignment
<table>
<tr>
<th>Option</th>
<th>Meaning</th>
</tr>
<tr>
<td><code>'<'</code></td>
<td>
Forces the field to be left-aligned within the available space (this is the
default for most objects).
</td>
</tr>
<tr>
<td><code>'>'</code></td>
<td>
Forces the field to be right-aligned within the available space (this is
the default for numbers).
</td>
</tr>
<tr>
<td><code>'^'</code></td>
<td>Forces the field to be centered within the available space.</td>
</tr>
</table>
The *align* field selects where padding is placed when *width* makes the
field wider than the value's natural rendering.
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.
| Option | Effect |
|--------|-------------------------------------------------------------------|
| `<` | Left-align; pad on the right. Default for non-numeric types. |
| `>` | Right-align; pad on the left. Default for numeric types. |
| `^` | Center the value; if the padding cannot be split evenly, the extra padding character goes on the right. |
The *sign* option is only valid for floating point and signed integer types,
and can be one of the following:
The *fill* character is any single Unicode code point other than `{` or `}`,
encoded the same way as the format string. It supplies the padding character
in place of the default space. A fill character is recognized only when it is
immediately followed by an *align* character — otherwise it would be
indistinguishable from an option in another position — so to use a custom
fill you must also specify an alignment.
<table>
<tr>
<th>Option</th>
<th>Meaning</th>
</tr>
<tr>
<td><code>'+'</code></td>
<td>
Indicates that a sign should be used for both nonnegative as well as
negative numbers.
</td>
</tr>
<tr>
<td><code>'-'</code></td>
<td>
Indicates that a sign should be used only for negative numbers (this is the
default behavior).
</td>
</tr>
<tr>
<td>space</td>
<td>
Indicates that a leading space should be used on nonnegative numbers, and a
minus sign on negative numbers.
</td>
</tr>
</table>
Alignment has no observable effect when the value's natural rendering is
already at least as wide as *width*; the value is never truncated to fit.
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.
```c++
fmt::format("[{:<10}]", "42"); // Result: "[42 ]"
fmt::format("[{:>10}]", "42"); // Result: "[ 42]"
fmt::format("[{:^10}]", "42"); // Result: "[ 42 ]"
fmt::format("[{:*^10}]", "42"); // Result: "[****42****]" -- '*' as fill
```
*width* is a decimal integer defining the minimum field width. If not
specified, then the field width will be determined by the content.
### Sign
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. This option is ignored when any alignment specifier is present.
The *sign* field controls how the sign of a numeric value is emitted. It
applies to signed integer and floating-point types only.
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.
| Option | Effect |
|--------|-------------------------------------------------------------------|
| `+` | Always emit a sign (`+` for nonnegative values, `-` for negative).|
| `-` | Emit `-` only for negative values. This is the default. |
| space | Emit a leading space for nonnegative values and `-` for negative ones; useful for aligning columns of signed numbers. |
The `'L'` option uses the current locale setting to insert the appropriate
number separator characters. This option is only valid for numeric types.
The sign of `-0.0` is preserved in floating-point output.
Finally, the *type* determines how the data should be presented.
```c++
fmt::format("{:+d} {:+d}", 7, -7); // Result: "+7 -7"
fmt::format("{: d} {: d}", 7, -7); // Result: " 7 -7"
```
The available string presentation types are:
### Alternate form (`#`)
<table>
<tr>
<th>Type</th>
<th>Meaning</th>
</tr>
<tr>
<td><code>'s'</code></td>
<td>
String format. This is the default type for strings and may be omitted.
</td>
</tr>
<tr>
<td><code>'?'</code></td>
<td>Debug format. The string is quoted and special characters escaped.</td>
</tr>
<tr>
<td>none</td>
<td>The same as <code>'s'</code>.</td>
</tr>
</table>
The `#` flag selects an *alternate form* whose exact meaning depends on the
presentation type:
The available character presentation types are:
- For integers rendered in binary, octal, or hexadecimal, it prepends the
appropriate base prefix (`0b`/`0B`, `0`, or `0x`/`0X`). The case of the
prefix follows the case of the type specifier — `0x` for `x`, `0X` for
`X`, and so on.
- For floating-point values, it forces the radix character to appear in the
output even if no fractional digits would otherwise be emitted, and
prevents the `g`/`G` presentation types from removing trailing zeros from
the significand.
<table>
<tr>
<th>Type</th>
<th>Meaning</th>
</tr>
<tr>
<td><code>'c'</code></td>
<td>
Character format. This is the default type for characters and may be
omitted.
</td>
</tr>
<tr>
<td><code>'?'</code></td>
<td>Debug format. The character is quoted and special characters escaped.</td>
</tr>
<tr>
<td>none</td>
<td>The same as <code>'c'</code>.</td>
</tr>
</table>
The `#` flag is not accepted by non-numeric types.
The available integer presentation types are:
### Zero padding (`0`)
<table>
<tr>
<th>Type</th>
<th>Meaning</th>
</tr>
<tr>
<td><code>'b'</code></td>
<td>
Binary format. Outputs the number in base 2. Using the <code>'#'</code>
option with this type adds the prefix <code>"0b"</code> to the output value.
</td>
</tr>
<tr>
<td><code>'B'</code></td>
<td>
Binary format. Outputs the number in base 2. Using the <code>'#'</code>
option with this type adds the prefix <code>"0B"</code> to the output value.
</td>
</tr>
<tr>
<td><code>'c'</code></td>
<td>Character format. Outputs the number as a character.</td>
</tr>
<tr>
<td><code>'d'</code></td>
<td>Decimal integer. Outputs the number in base 10.</td>
</tr>
<tr>
<td><code>'o'</code></td>
<td>Octal format. Outputs the number in base 8.</td>
</tr>
<tr>
<td><code>'x'</code></td>
<td>
Hex format. Outputs the number in base 16, using lower-case letters for the
digits above 9. Using the <code>'#'</code> option with this type adds the
prefix <code>"0x"</code> to the output value.
</td>
</tr>
<tr>
<td><code>'X'</code></td>
<td>
Hex format. Outputs the number in base 16, using upper-case letters for the
digits above 9. Using the <code>'#'</code> option with this type adds the
prefix <code>"0X"</code> to the output value.
</td>
</tr>
<tr>
<td>none</td>
<td>The same as <code>'d'</code>.</td>
</tr>
</table>
A `0` placed immediately before *width* enables sign-aware zero padding for
numeric types. Zeros are inserted between the sign (or base prefix, if any)
and the most significant digit, so that a sign or `0x` prefix stays adjacent
to the digits rather than being separated by spaces. For example, `{:+08d}`
applied to `120` produces `+0000120`.
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.
Zero padding:
The available presentation types for floating-point values are:
- applies only to numeric types;
- has no effect on `inf` or `nan`;
- is silently ignored when an explicit *align* is also present.
<table>
<tr>
<th>Type</th>
<th>Meaning</th>
</tr>
<tr>
<td><code>'a'</code></td>
<td>
Hexadecimal floating point format. Prints the number in base 16 with
prefix <code>"0x"</code> and lower-case letters for digits above 9.
Uses <code>'p'</code> to indicate the exponent.
</td>
</tr>
<tr>
<td><code>'A'</code></td>
<td>
Same as <code>'a'</code> except it uses upper-case letters for the
prefix, digits above 9 and to indicate the exponent.
</td>
</tr>
<tr>
<td><code>'e'</code></td>
<td>
Exponent notation. Prints the number in scientific notation using
the letter 'e' to indicate the exponent.
</td>
</tr>
<tr>
<td><code>'E'</code></td>
<td>
Exponent notation. Same as <code>'e'</code> except it uses an
upper-case <code>'E'</code> as the separator character.
</td>
</tr>
<tr>
<td><code>'f'</code></td>
<td>Fixed point. Displays the number as a fixed-point number.</td>
</tr>
<tr>
<td><code>'F'</code></td>
<td>
Fixed point. Same as <code>'f'</code>, but converts <code>nan</code>
to <code>NAN</code> and <code>inf</code> to <code>INF</code>.
</td>
</tr>
<tr>
<td><code>'g'</code></td>
<td>
<p>General format. For a given precision <code>p &gt;= 1</code>,
this rounds the number to <code>p</code> significant digits and then
formats the result in either fixed-point format or in scientific
notation, depending on its magnitude.</p>
<p>A precision of <code>0</code> is treated as equivalent to a precision
of <code>1</code>.</p>
</td>
</tr>
<tr>
<td><code>'G'</code></td>
<td>
General format. Same as <code>'g'</code> except switches to
<code>'E'</code> if the number gets too large. The representations of
infinity and NaN are uppercased, too.
</td>
</tr>
<tr>
<td>none</td>
<td>
Similar to <code>'g'</code>, except that the default precision is as
high as needed to represent the particular value.
</td>
</tr>
</table>
### Width
The available presentation types for pointers are:
*width* is a non-negative decimal integer giving the minimum number of
characters that the field should occupy. If the formatted value is shorter
than *width*, it is padded according to *align* and *fill*; if it is longer,
the value is written in full. *width* never causes the value to be
truncated.
<table>
<tr>
<th>Type</th>
<th>Meaning</th>
</tr>
<tr>
<td><code>'p'</code></td>
<td>
Pointer format. This is the default type for pointers and may be omitted.
</td>
</tr>
<tr>
<td>none</td>
<td>The same as <code>'p'</code>.</td>
</tr>
</table>
To supply *width* at runtime, write the field as `{}` to consume the next
argument, or as `{arg_id}` to reference an integer argument by position or
by name.
When formatting strings, "width" is measured in display columns using a
Unicode-aware estimate (East Asian wide and fullwidth characters, plus
common emoji ranges, count as two columns; everything else counts as one).
This keeps fixed *width* values visually consistent in monospace renderings
that combine Latin and CJK text.
```c++
fmt::format("[{:6}]", 42); // Result: "[ 42]" -- right-aligned by default
fmt::format("[{:6}]", "hi"); // Result: "[hi ]" -- left-aligned by default
fmt::format("[{:{}}]", 42, 6); // Result: "[ 42]" -- width from an argument
```
### Precision
*precision* is a non-negative decimal integer (introduced by `.`) whose
meaning depends on the value being formatted. As with *width*, it may be
supplied as a nested replacement field for runtime evaluation.
| Type | Meaning of `.precision` |
|-------------------------------|-----------------------------------------------|
| `e`, `E`, `f`, `F` | Digits emitted after the radix character. |
| `g`, `G` | Total number of significant digits. |
| `a`, `A` | Digits after the radix character in the hexadecimal significand. If omitted, just enough digits are emitted to round-trip the value exactly. |
| Strings (`s`, `?`, or default) | Upper bound on the number of code points copied from the value. |
A *precision* is not accepted for integer, character, boolean, or pointer
types. When a *precision* limits the number of characters taken from a C
string, the string must still be null-terminated.
```c++
fmt::format("{:.2f}", 3.14159); // Result: "3.14"
fmt::format("{:.3g}", 3.14159); // Result: "3.14"
fmt::format("{:.4}", "hello, world"); // Result: "hell"
fmt::format("{:.{}f}", 3.14159, 4); // Result: "3.1416" -- precision from an argument
```
### Locale (`L`)
The `L` flag selects locale-sensitive formatting for numeric types. The
formatter inspects the C++ locale supplied to the formatting function (or
the global locale, if none was passed) and inserts the locale's digit
grouping characters and — for floating-point values — its radix character.
The flag has no effect on non-numeric types.
```c++
auto loc = std::locale("en_US.UTF-8");
fmt::format(loc, "{:L}", 1234567890); // Result: "1,234,567,890"
fmt::format(loc, "{:.2Lf}", 1234567.89); // Result: "1,234,567.89"
```
### Presentation type
The *type* field chooses the representation for the value. Specifiers are
grouped below by the value categories they apply to.
**Integers, booleans, and characters:**
| Type | Effect |
|------|---------------------------------------------------------------------|
| `b` | Base 2. The `#` flag adds a `0b` prefix. |
| `B` | Base 2. The `#` flag adds a `0B` prefix. |
| `c` | Render the integer as the character with that code point. Not allowed for `bool`. |
| `d` | Base 10. The default for integer types. |
| `o` | Base 8. |
| `x` | Base 16, lower-case digits. The `#` flag adds a `0x` prefix. |
| `X` | Base 16, upper-case digits. The `#` flag adds a `0X` prefix. |
| none | Same as `d` for integers, `c` for characters, and the textual form (`true`/`false`) for `bool`. |
```c++
fmt::format("{:d} {:#x} {:#o} {:#b}", 42, 42, 42, 42);
// Result: "42 0x2a 052 0b101010"
fmt::format("{:#06x}", 0xfe); // # adds the prefix, 06 zero-pads to width 6
// Result: "0x00fe"
```
**Floating-point values:**
| Type | Effect |
|------|---------------------------------------------------------------------|
| `a` | Hexadecimal-significand form (e.g. `1.8p+1`). Lower-case digits and a lower-case `p` for the binary exponent. The `#` flag adds a `0x` prefix. |
| `A` | Same as `a`, but upper-case throughout. |
| `e` | Scientific notation with a lower-case `e` for the decimal exponent. |
| `E` | Scientific notation with an upper-case `E`. |
| `f` | Fixed-point notation. |
| `F` | Same as `f`, but renders `nan` as `NAN` and `inf` as `INF`. |
| `g` | General form: scientific notation when the exponent would be less than &minus;4 or not less than the precision, otherwise fixed-point; trailing zeros are removed from the fractional part unless `#` is set. A precision of `0` is interpreted as `1`. |
| `G` | Same as `g`, but uses `E` for the exponent and upper-case `INF`/`NAN`. |
| none | Shortest round-trip representation: the formatted value, when parsed back into the same floating-point type, reproduces the input bit for bit. |
**Strings and characters:**
| Type | Effect |
|------|---------------------------------------------------------------------|
| `s` | Plain string output. Default for string types and for `bool` (which is rendered as `true` or `false`). |
| `c` | Character output. Default for character types. Not allowed for `bool`. |
| `?` | Debug output: the value is wrapped in single quotes (characters) or double quotes (strings), and non-printable, non-ASCII, and special characters are escaped using C-style escape sequences such as `\n`, `\t`, `\"`, and `\u{...}`. |
| none | Same as `s` for strings and `bool`, and as `c` for characters. |
```c++
fmt::format("{}", "tab\there"); // Result contains a literal tab character.
fmt::format("{:?}", "tab\there"); // Result: "\"tab\\there\""
```
**Pointers:**
| Type | Effect |
|------|---------------------------------------------------------------------|
| `p` | Hexadecimal address prefixed by `0x`. Default for pointer types. |
| none | Same as `p`. |
A C string (`char*` or `const char*`) accepts both the string presentation
types and `p`, so the same value can be formatted as either text or an
address.
## Chrono Format Specifications
@ -713,6 +601,22 @@ The available padding modifiers (*padding_modifier*) are:
These modifiers are only supported for the `'H'`, `'I'`, `'M'`, `'S'`, `'U'`,
`'V'`, `'W'`, `'Y'`, `'d'`, `'j'` and `'m'` presentation types.
Example:
```c++
#include <fmt/chrono.h>
auto t = std::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
```
## Range Format Specifications
Format specifications for range types have the following syntax:
@ -765,87 +669,13 @@ fmt::print("{:n:f}", std::array{std::numbers::pi, std::numbers::e});
// Output: 3.141593, 2.718282
```
## Format Examples
<a id="format-examples"></a>
## 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:
```c++
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:
```c++
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:
```c++
fmt::format("{:<{}}", "left aligned", 30);
// Result: "left aligned "
```
Dynamic precision:
```c++
fmt::format("{:.{}f}", 3.14, 1);
// Result: "3.1"
```
Replacing `%+f`, `%-f`, and `% f` and specifying a sign:
```c++
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:
```c++
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:
```c++
fmt::format("{:#04x}", 0);
// Result: "0x00"
```
Box drawing using Unicode fill:
Most of the format options are introduced alongside their grammar in the
sections above. The example below combines several of them — nested
replacement fields, fill characters, and centering — to draw a fixed-width
box around a message:
```c++
fmt::print(
@ -854,35 +684,10 @@ fmt::print(
"└{0:─^{2}}┘\n", "", "Hello, world!", 20);
```
prints:
Output:
```
┌────────────────────┐
│ Hello, world! │
└────────────────────┘
```
Using type-specific formatting:
```c++
#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:
```c++
#include <fmt/format.h>
auto s = fmt::format(std::locale("en_US.UTF-8"), "{:L}", 1234567890);
// s == "1,234,567,890"
```