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Victor Zverovich 2026-06-02 09:04:13 -07:00
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@ -101,10 +101,10 @@ 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. already at least as wide as *width*; the value is never truncated to fit.
```c++ ```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]"
fmt::format("[{:^10}]", "42"); // Result: "[ 42 ]" fmt::format("[{:^10}]", "42"); // Result: "[ 42 ]"
fmt::format("[{:*^10}]", "42"); // Result: "[****42****]" -- '*' as fill fmt::format("[{:*^10}]", "42"); // Result: "[****42****]" -- '*' as fill
``` ```
### Sign ### Sign
@ -121,8 +121,8 @@ applies to signed integer and floating-point types only.
The sign of `-0.0` is preserved in floating-point output. The sign of `-0.0` is preserved in floating-point output.
```c++ ```c++
fmt::format("{:+d} {:+d}", 7, -7); // Result: "+7 -7" fmt::format("{:+d} {:+d}", 7, -7); // Result: "+7 -7"
fmt::format("{: d} {: d}", 7, -7); // Result: " 7 -7" fmt::format("{: d} {: d}", 7, -7); // Result: " 7 -7"
``` ```
### Alternate form (`#`) ### Alternate form (`#`)
@ -134,7 +134,7 @@ presentation type:
appropriate base prefix (`0b`/`0B`, `0`, or `0x`/`0X`). The case of 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 prefix follows the case of the type specifier — `0x` for `x`, `0X` for
`X`, and so on. `X`, and so on.
- For floating-point values, it forces the radix character to appear in the - For floating-point values, it forces the decimal point to appear in the
output even if no fractional digits would otherwise be emitted, and output even if no fractional digits would otherwise be emitted, and
prevents the `g`/`G` presentation types from removing trailing zeros from prevents the `g`/`G` presentation types from removing trailing zeros from
the significand. the significand.
@ -153,7 +153,7 @@ Zero padding:
- applies only to numeric types; - applies only to numeric types;
- has no effect on `inf` or `nan`; - has no effect on `inf` or `nan`;
- is silently ignored when an explicit *align* is also present. - is ignored when an explicit *align* is also present.
### Width ### Width
@ -174,9 +174,9 @@ This keeps fixed *width* values visually consistent in monospace renderings
that combine Latin and CJK text. that combine Latin and CJK text.
```c++ ```c++
fmt::format("[{:6}]", 42); // Result: "[ 42]" -- right-aligned by default fmt::format("[{:6}]", 42); // Result: "[ 42]" -- right-aligned by default
fmt::format("[{:6}]", "hi"); // Result: "[hi ]" -- left-aligned by default fmt::format("[{:6}]", "hi"); // Result: "[hi ]" -- left-aligned by default
fmt::format("[{:{}}]", 42, 6); // Result: "[ 42]" -- width from an argument fmt::format("[{:{}}]", 42, 6); // Result: "[ 42]" -- width from an argument
``` ```
### Precision ### Precision
@ -187,9 +187,9 @@ supplied as a nested replacement field for runtime evaluation.
| Type | Meaning of `.precision` | | Type | Meaning of `.precision` |
|-------------------------------|-----------------------------------------------| |-------------------------------|-----------------------------------------------|
| `e`, `E`, `f`, `F` | Digits emitted after the radix character. | | `e`, `E`, `f`, `F` | Digits emitted after the decimal point. |
| `g`, `G` | Total number of significant digits. | | `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. | | `a`, `A` | Digits after the decimal point 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. | | 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 A *precision* is not accepted for integer, character, boolean, or pointer
@ -197,10 +197,10 @@ types. When a *precision* limits the number of characters taken from a C
string, the string must still be null-terminated. string, the string must still be null-terminated.
```c++ ```c++
fmt::format("{:.2f}", 3.14159); // Result: "3.14" fmt::format("{:.2f}", 3.14159); // Result: "3.14"
fmt::format("{:.3g}", 3.14159); // Result: "3.14" fmt::format("{:.3g}", 3.14159); // Result: "3.14"
fmt::format("{:.4}", "hello, world"); // Result: "hell" fmt::format("{:.4}", "hello, world"); // Result: "hell"
fmt::format("{:.{}f}", 3.14159, 4); // Result: "3.1416" -- precision from an argument fmt::format("{:.{}f}", 3.14159, 4); // Result: "3.1416" -- precision from an argument
``` ```
### Locale (`L`) ### Locale (`L`)
@ -208,7 +208,7 @@ fmt::format("{:.{}f}", 3.14159, 4); // Result: "3.1416" -- precision from an ar
The `L` flag selects locale-sensitive formatting for numeric types. The The `L` flag selects locale-sensitive formatting for numeric types. The
formatter inspects the C++ locale supplied to the formatting function (or formatter inspects the C++ locale supplied to the formatting function (or
the global locale, if none was passed) and inserts the locale's digit the global locale, if none was passed) and inserts the locale's digit
grouping characters and — for floating-point values — its radix character. grouping characters and — for floating-point values — its decimal point.
The flag has no effect on non-numeric types. The flag has no effect on non-numeric types.
```c++ ```c++
@ -239,7 +239,7 @@ grouped below by the value categories they apply to.
fmt::format("{:d} {:#x} {:#o} {:#b}", 42, 42, 42, 42); fmt::format("{:d} {:#x} {:#o} {:#b}", 42, 42, 42, 42);
// Result: "42 0x2a 052 0b101010" // Result: "42 0x2a 052 0b101010"
fmt::format("{:#06x}", 0xfe); // # adds the prefix, 06 zero-pads to width 6 fmt::format("{:#06x}", 0xfe); // # adds the prefix, 06 zero-pads to width 6
// Result: "0x00fe" // Result: "0x00fe"
``` ```