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Difference between revisions of "cpp/utility/format/vformat to"

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< cpp‎ | utility‎ | format
m
m (fmt)
 
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{{dcl begin}}
 
{{dcl begin}}
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{{dcl header | format }}
+
{{dcl header|format}}
−
{{dcl | num=1 | since=c++20 |1=
+
{{dcl|num=1|since=c++20|1=
 
template< class OutputIt >
 
template< class OutputIt >
 
OutputIt vformat_to( OutputIt out, std::string_view fmt, std::format_args args );
 
OutputIt vformat_to( OutputIt out, std::string_view fmt, std::format_args args );
 
}}
 
}}
−
{{dcl | num=2 | since=c++20 |1=
+
{{dcl|num=2|since=c++20|1=
 
template< class OutputIt >
 
template< class OutputIt >
 
OutputIt vformat_to( OutputIt out, std::wstring_view fmt, std::wformat_args args );
 
OutputIt vformat_to( OutputIt out, std::wstring_view fmt, std::wformat_args args );
 
}}
 
}}
−
{{dcl | num=3 | since=c++20 |1=
+
{{dcl|num=3|since=c++20|1=
 
template< class OutputIt >
 
template< class OutputIt >
 
OutputIt vformat_to( OutputIt out, const std::locale& loc,
 
OutputIt vformat_to( OutputIt out, const std::locale& loc,
 
                     std::string_view fmt, std::format_args args );
 
                     std::string_view fmt, std::format_args args );
 
}}
 
}}
−
{{dcl | num=4 | since=c++20 |1=
+
{{dcl|num=4|since=c++20|1=
 
template< class OutputIt >
 
template< class OutputIt >
 
OutputIt vformat_to( OutputIt out, const std::locale& loc,
 
OutputIt vformat_to( OutputIt out, const std::locale& loc,
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{{dcl end}}
 
{{dcl end}}
  
−
Format arguments held by {{tt|args}} according to the format string {{tt|fmt}}, and write the result to the output iterator {{tt|out}}. If present, {{tt|loc}} is used for locale-specific formatting.
+
Format arguments held by {{c|args}} according to the format string {{c|fmt}}, and write the result to the output iterator {{c|out}}. If present, {{c|loc}} is used for locale-specific formatting.
  
−
Let {{tt|CharT}} be {{c|decltype(fmt)::char_type}} ({{c|char}} for overloads {{v|1,3}}, {{c|wchar_t}} for overloads {{v|2,4}}).
+
Let {{tt|CharT}} be {{c/core|decltype(fmt)::char_type}} ({{c/core|char}} for overloads {{v|1,3}}, {{c/core|wchar_t}} for overloads {{v|2,4}}).
  
 
{{cpp/enable if|plural=true|
 
{{cpp/enable if|plural=true|
−
{{tt|OutputIt}} satisfies the concept {{c|std::output_iterator<const CharT&>}}.
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{{tt|OutputIt}} satisfies the concept {{c/core|std::output_iterator<const CharT&>}}.}}
−
}}
+
{{cpp/precondition|
−
The behavior is undefined if {{tt|OutputIt}} does not model (meet the semantic requirements of) the concept {{c|std::output_iterator<const CharT&>}}, or if {{c|std::formatter<Ti, CharT>}} does not meet the {{named req|Formatter}} requirements for any {{tt|Ti}} in the type of arguments.
+
{{tt|OutputIt}} must model (meet the semantic requirements of) the concept {{c/core|std::output_iterator<const CharT&>}}, and {{c/core|std::formatter<Ti, CharT>}} must meet the {{named req|Formatter}} requirements for any {{tt|Ti}} in the type of arguments.}}
  
 
===Parameters===
 
===Parameters===
 
{{par begin}}
 
{{par begin}}
−
{{par | out | iterator to the output buffer}}
+
{{par|out|iterator to the output buffer}}
−
{{par | fmt | {{cpp/utility/format/format string}} }}
+
{{par|fmt|{{cpp/utility/format/format string}}}}
−
{{par | args | arguments to be formatted}}
+
{{par|args|arguments to be formatted}}
−
{{par | loc | {{lc|std::locale}} used for locale-specific formatting}}
+
{{par|loc|{{lc|std::locale}} used for locale-specific formatting}}
 
{{par end}}
 
{{par end}}
  
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===Exceptions===
 
===Exceptions===
−
Throws {{lc|std::format_error}} if {{tt|fmt}} is not a valid format string for the provided arguments. Also propagates any exception thrown by formatter or iterator operations.
+
Throws {{lc|std::format_error}} if {{c|fmt}} is not a valid format string for the provided arguments. Also propagates any exception thrown by formatter or iterator operations.
  
 
===Example===
 
===Example===
 
{{example
 
{{example
−
|code=
+
|code=
−
|output=
+
|output=
 
}}
 
}}
  
 
===Defect reports===
 
===Defect reports===
 
{{dr list begin}}
 
{{dr list begin}}
−
{{dr list item|paper=P2216R3|std=C++20|before=type of {{tt|args}} is parameterized on {{tt|OutputIt}}|after=not parameterized}}
+
{{dr list item|paper=P2216R3|std=C++20|before=type of {{c|args}} is parameterized on {{tt|OutputIt}}|after=not parameterized}}
 
{{dr list end}}
 
{{dr list end}}
  

Latest revision as of 13:23, 9 July 2024

 
C++
 
Utilities library
General utilities
Relational operators (deprecated in C++20)
 
Formatting library
Standard format specification
Formatting functions
(C++20)
(C++20)
(C++20)
(C++20)
(C++20)
vformat_to
(C++20)
Format strings
(C++20)(C++20)(C++20)
(C++26)
Formatting concepts
(C++23)
Formatter
(C++20)
(C++23)
(C++23)
(C++23)
(C++23)
(C++20)(C++20)(C++20)
(C++20)(C++20)(C++20)
(C++23)
(C++23)
Formatting arguments
(C++20)
(C++20)
(C++20)(C++20)(C++20)
(C++20) (deprecated in C++26)
(C++20)(C++20)
Format error
(C++20)
 
Defined in header <format>
template< class OutputIt >
OutputIt vformat_to( OutputIt out, std::string_view fmt, std::format_args args );
 (1) (since C++20)
template< class OutputIt >
OutputIt vformat_to( OutputIt out, std::wstring_view fmt, std::wformat_args args );
 (2) (since C++20)
template< class OutputIt >

OutputIt vformat_to( OutputIt out, const std::locale& loc,

                     std::string_view fmt, std::format_args args );
 (3) (since C++20)
template< class OutputIt >

OutputIt vformat_to( OutputIt out, const std::locale& loc,

                     std::wstring_view fmt, std::wformat_args args );
 (4) (since C++20)

Format arguments held by args according to the format string fmt, and write the result to the output iterator out. If present, loc is used for locale-specific formatting.

Let CharT be decltype(fmt)::char_type (char for overloads (1,3), wchar_t for overloads (2,4)).

These overloads participate in overload resolution only if OutputIt satisfies the concept std::output_iterator<const CharT&>.

OutputIt must model (meet the semantic requirements of) the concept std::output_iterator<const CharT&>, and std::formatter<Ti, CharT> must meet the Formatter requirements for any Ti in the type of arguments. Otherwise, the behavior is undefined.

Contents

[edit] Parameters

out - iterator to the output buffer
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-id s 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. Cannot start with }.

(since C++23)
(since C++26)
  • For other formattable types, the format specification is determined by user-defined formatter specializations.
args - arguments to be formatted
loc - std::locale used for locale-specific formatting

[edit] Return value

Iterator past the end of the output range.

[edit] Exceptions

Throws std::format_error if fmt is not a valid format string for the provided arguments. Also propagates any exception thrown by formatter or iterator operations.

[edit] Example

This section is incomplete
Reason: no example

[edit] Defect reports

The following behavior-changing defect reports were applied retroactively to previously published C++ standards.

DR Applied to Behavior as published Correct behavior
P2216R3 C++20 type of args is parameterized on OutputIt not parameterized

[edit] See also

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