std::basic_format_parse_context - cppreference.com (original) (raw)
| | | | | ------------------------------------------------------------- | | ------------- | | template< class CharT > class basic_format_parse_context; | | (since C++20) |
Provides access to the format string parsing state consisting of the format string range being parsed and the argument counter for automatic indexing.
A std::basic_format_parse_context instance is passed to Formatter when parsing the format specification.
A program that declares an explicit or partial specialization of std::basic_format_parse_context is ill-formed, no diagnostic required.
Several typedefs for common character types are provided:
| Type | Definition |
| std::format_parse_context | std::basic_format_parse_context<char> |
| std::wformat_parse_context | std::basic_format_parse_context<wchar_t> |
Contents
- 1 Member types
- 2 Member functions
- 3 std::basic_format_parse_context::basic_format_parse_context
- 4 std::basic_format_parse_context::begin
- 5 std::basic_format_parse_context::end
- 6 std::basic_format_parse_context::advance_to
- 7 std::basic_format_parse_context::next_arg_id
- 8 std::basic_format_parse_context::check_arg_id
- 9 std::basic_format_parse_context::check_dynamic_spec
- 10 std::basic_format_parse_context::check_dynamic_spec_integral
- 11 std::basic_format_parse_context::check_dynamic_spec_string
[edit] Member types
[edit] Member functions
| (constructor) | constructs a std::basic_format_parse_context instance from format string and argument count (public member function) |
|---|---|
| operator=[deleted] | std::basic_format_parse_context is not copyable (public member function) |
| begin | returns an iterator to the beginning of the format string range (public member function) |
| end | returns an iterator to the end of the format string range (public member function) |
| advance_to | advances the begin iterator to the given position (public member function) |
| next_arg_id | enters automatic indexing mode, and returns the next argument index (public member function) |
| check_arg_id | enters manual indexing mode, checks if the given argument index is in range (public member function) |
| check_dynamic_spec(C++26) | checks if the type of the corresponding format argument with the given argument index is in the given type template arguments (public member function) |
| check_dynamic_spec_integral(C++26) | checks if the type of the corresponding format argument with the given argument index is an integral type (public member function) |
| check_dynamic_spec_string(C++26) | checks if the type of the corresponding format argument with the given argument index is a string type (public member function) |
std::basic_format_parse_context::basic_format_parse_context
| (1) | ||
|---|---|---|
| constexpr explicit basic_format_parse_context( std::basic_string_view<CharT> fmt, std::size_t num_args = 0 ) noexcept; | (until C++26) | |
| constexpr explicit basic_format_parse_context( std::basic_string_view<CharT> fmt ) noexcept; | (since C++26) | |
| basic_format_parse_context( const basic_format_parse_context& ) = delete; | (2) |
- Constructs a
std::basic_format_parse_contextinstance. Initializes the format string range to[fmt.begin(),fmt.end()), and the argument count to num_args(until C++26)0(since C++26).
| Any call to next_arg_id, check_arg_id, or check_dynamic_spec on an instance of std::basic_format_parse_context initialized using this constructor is not a core constant expression. | (since C++26) |
|---|
- The copy constructor is deleted.
std::basic_format_parse_contextis not copyable.
std::basic_format_parse_context::begin
| constexpr const_iterator begin() const noexcept; | | | | ------------------------------------------------- | | |
Returns an iterator to the beginning of the format string range.
std::basic_format_parse_context::end
| constexpr const_iterator end() const noexcept; | | | | ----------------------------------------------- | | |
Returns an iterator to the end of the format string range.
std::basic_format_parse_context::advance_to
| constexpr void advance_to( const_iterator it ); | | | | ------------------------------------------------- | | |
Sets the beginning of the format string range to it. After a call to advance_to(), subsequent calls to begin() will return a copy of it.
The behavior is undefined if end() is not reachable from it.
std::basic_format_parse_context::next_arg_id
Enters automatic argument indexing mode, and returns the next argument index, starting from 0.
If *this has already entered manual argument indexing mode, throws std::format_error.
If the next argument index is larger than or equal to the num_args provided in the constructor, the call is not a core constant expression.
std::basic_format_parse_context::check_arg_id
Enters manual argument indexing mode.
If *this has already entered automatic argument indexing mode, throws std::format_error.
If id is larger than or equal to the num_args provided in the constructor, the call is not a core constant expression.
std::basic_format_parse_context::check_dynamic_spec
| template< class... Ts > constexpr void check_dynamic_spec( std::size_t id ) noexcept; | | (since C++26) | | ---------------------------------------------------------------------------------------------------------------------- | | ------------- |
If id is larger than or equal to the num_args provided in the constructor or the type of the corresponding format argument (after conversion to std::basic_format_arg) is not one of the types in Ts..., the call is not a core constant expression. A call to check_dynamic_spec has no effect at runtime.
The program is ill-formed unless sizeof...(Ts) >= 1, the types in Ts... are unique, and each type is one of bool, char_type, int, unsigned int, long long int, unsigned long long int, float, double, long double, const char_type*, std::basic_string_view<char_type>, or const void*.
std::basic_format_parse_context::check_dynamic_spec_integral
| constexpr void check_dynamic_spec_integral( std::size_t id ) noexcept; | | (since C++26) | | ------------------------------------------------------------------------------------------------------- | | ------------- |
Equivalent to call check_dynamic_spec<int, unsigned int, long long int, unsigned long long int>(id). A call to check_dynamic_spec_integral has no effect at runtime.
std::basic_format_parse_context::check_dynamic_spec_string
| constexpr void check_dynamic_spec_string( std::size_t id ) noexcept; | | (since C++26) | | ----------------------------------------------------------------------------------------------------- | | ------------- |
Equivalent to call check_dynamic_spec<const char_type*, std::basic_string_view<char_type>>(id). A call to check_dynamic_spec_string has no effect at runtime.
[edit] 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 |
|---|---|---|---|
| LWG 3825 | C++20 | check_arg_id has a compile-time argumentid check, but next_arg_id did not have | added |
| LWG 3975 | C++20 | user specialization of basic_format_parse_context was allowed | disallowed |