# vprint_unicode(std::ostream)

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< cpp‎ | io‎ | basic ostream

Defined in header `<ostream>` |  |
void vprint_unicode( std::ostream& os, std::string_view fmt, std::format_args args ); |  | (since C++23)

Behaves as FormattedOutputFunction (except that some details of error reporting differ):

- First, the function constructs and checks the sentry object.
- Then, initializes an automatic variable as if by std::string out = std::vformat(os.getloc(), fmt, args);.
- Finally, inserts the character sequence `[out.begin(), out.end())` into os, that is, if os refers to a terminal capable of displaying Unicode, writes out to this terminal using the native Unicode API. Otherwise, writes unmodified out to the os.

### Parameters

os | - | output stream to insert data into
fmt | - | an object that represents the format string. The format string consists of ordinary characters (except { and }), which are copied unchanged to the output, escape sequences {{ and }}, which are replaced with { and } respectively in the output, and replacement fields. Each replacement field has the following format:
`{` arg-id (optional) `}` | (1) |
`{` arg-id (optional) `:` format-spec `}` | (2) |
1) replacement field without a format specification 2) replacement field with a format specification
arg-id | - | specifies the index of the argument in `args` whose value is to be used for formatting; if it is omitted, the arguments are used in order. The arg-ids in a format string must all be present or all be omitted. Mixing manual and automatic indexing is an error.
format-spec | - | the format specification defined by the std::formatter specialization for the corresponding argument.
For basic types and standard string types, the format specification is interpreted as standard format specification. For chrono types, the format specification is interpreted as chrono format specification. For std::thread::id, the format specification is interpreted as thread id format specification. For other formattable types, the format specification is determined by user-defined `formatter` specializations.
args | - | arguments to be formatted

### Return value

(none)

### Exceptions

- std::bad_alloc on allocation failure.
- Propagate any exception thrown by any formatter, e.g. std::format_error, without regard to the value of os.exceptions() and without turning on ios_base::badbit in the error state of os.
- May throw ios_base::failure caused by os.setstate(ios_base::badbit) which is called if an insertion into os fails.

### Notes

If invoking the native Unicode API requires transcoding, the invalid code units are substituted with `U+FFFD` REPLACEMENT CHARACTER (see "The Unicode Standard Version 14.0 - Core Specification", Chapter 3.9).

Feature-test macro | Value | Std | Comment
--- | --- | --- | ---
`__cpp_lib_print` | 202207L | (C++23) | Formatted output
`__cpp_lib_format` | 202207L | (C++23) | Exposing std::basic_format_string

### Example

| This section is incomplete Reason: no example

### See also

vprint_nonunicode(std::ostream) (C++23) | outputs character data using type-erased argument representation (function)
print(std::ostream) (C++23) | outputs formatted representation of the arguments (function template)
operator<<(std::basic_ostream) | inserts character data or insert into rvalue stream (function template)
vprint_unicode (C++23) | prints to Unicode capable stdout or a file stream using type-erased argument representation (function)
format (C++20) | stores formatted representation of the arguments in a new string (function template)

### External links

1. | Unicode
2. | The Unicode Standard Version 14.0 - Core Specification

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