標準庫標頭檔案 <format> (C++20)

 

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語言支援 <cfloat> <climits> <compare> (C++20) <contracts> (C++26) <coroutine> (C++20) <csetjmp> <csignal> <cstdarg> <cstddef> <cstdint> (C++11) <cstdlib> <exception> <initializer_list> (C++11)    <limits> <new> <source_location> (C++20) <stdfloat> (C++23) <typeinfo> <version> (C++20) 概念 <concepts> (C++20) 診斷 <cassert> <cerrno> <debugging> (C++26) <stacktrace> (C++23) <stdexcept> <system_error> (C++11) 記憶體管理 <memory> <memory_resource> (C++17) <scoped_allocator> (C++11) 超程式設計 <type_traits> (C++11) <ratio> (C++11)

通用工具 <any> (C++17) <bitset> <bit> (C++20) <charconv> (C++17) <expected> (C++23) <format> (C++20) <functional> <optional> (C++17) <tuple> (C++11) <typeindex> (C++11) <utility> <variant> (C++17) 容器 <array> (C++11) <deque> <flat_map> (C++23) <flat_set> (C++23) <forward_list> (C++11) <hive> (C++26) <inplace_vector> (C++26)    <list> <map> <mdspan> (C++23) <queue> <set> <span> (C++20) <stack> <unordered_map> (C++11) <unordered_set> (C++11) <vector> 迭代器 <iterator> Ranges <generator> (C++23) <ranges> (C++20)

演算法 <algorithm> <numeric> 字串 <cctype> <cstring> <cuchar> (C++11) <cwchar> <cwctype> <string_view> (C++17) <string> 文字處理 <clocale> <codecvt> (C++11/17/26*) <locale> <regex> (C++11) <text_encoding> (C++26)    數值 <cfenv> (C++11) <cmath> <complex> <linalg> (C++26) <numbers> (C++20) <random> (C++11) <simd> (C++26) <valarray> 時間 <chrono> (C++11) <ctime> C 相容性 <ccomplex> (C++11/17/20*) <ciso646> (直到 C++20) <cstdalign> (C++11/17/20*) <cstdbool> (C++11/17/20*) <ctgmath> (C++11/17/20*)

輸入/輸出 <cinttypes> (C++11) <cstdio> <filesystem> (C++17) <fstream> <iomanip> <iosfwd> <iostream> <ios> <istream> <ostream> <print> (C++23) <spanstream> (C++23) <sstream> <streambuf> <strstream> (C++98/26*) <syncstream> (C++20) 併發支援 <atomic> (C++11) <barrier> (C++20) <condition_variable> (C++11) <future> (C++11) <hazard_pointer> (C++26) <latch> (C++20) <mutex> (C++11) <rcu> (C++26) <semaphore> (C++20) <shared_mutex> (C++14) <stdatomic.h> (C++23) <stop_token> (C++20) <thread> (C++11) 執行支援 <execution> (C++17)

 

此標頭檔案是文字處理庫的一部分。

概念
formattable (C++23)	指定一個型別是可格式化的，即它特化了 std::formatter 並提供了成員函式 parse 和 format (概念)
列舉
range_format (C++23)	指定範圍應如何格式化 (列舉)
類
formatter (C++20)	定義給定型別的格式化規則 (類模板)
range_formatter (C++23)	有助於實現範圍型別的 std::formatter 特化的類模板 (類模板)
basic_format_parse_contextformat_parse_contextwformat_parse_context (C++20)(C++20)(C++20)	格式化字串解析器狀態 (類模板)
basic_format_contextformat_contextwformat_context (C++20)(C++20)(C++20)	格式化狀態，包括所有格式化引數和輸出迭代器 (類模板)
basic_format_arg (C++20)	為使用者定義格式化器提供格式化引數訪問的類模板 (類模板)
basic_format_argsformat_argswformat_args (C++20)(C++20)(C++20)	提供對所有格式化引數訪問的類 (類模板)
basic_format_stringformat_stringwformat_string (C++20)(C++20)(C++20)	在構造時執行編譯時格式字串檢查的類模板 (類模板)
format_error (C++20)	格式化錯誤時丟擲的異常型別 (類)
格式化器特化
std::formatter<pair-or-tuple> (C++23)	對 pair 和 tuple 的格式化支援 (類模板特化)
std::formatter<range> (C++23)	對範圍的格式化支援 (類模板特化)
函式
format (C++20)	將引數的格式化表示儲存在新字串中 (函式模板)
format_to (C++20)	透過輸出迭代器寫出其引數的格式化表示 (函式模板)
format_to_n (C++20)	透過輸出迭代器寫出其引數的格式化表示，不超過指定大小 (函式模板)
formatted_size (C++20)	確定儲存其引數格式化表示所需的字元數 (函式模板)
runtime_format (C++26)	建立可直接用於面向使用者的格式化函式的執行時格式字串 (函式)
vformat (C++20)	使用型別擦除引數表示的 std::format 的非模板變體 (函式)
vformat_to (C++20)	使用型別擦除引數表示的 std::format_to 的非模板變體 (函式模板)
visit_format_arg (C++20) (在 C++26 中廢棄)	使用者定義格式化器的引數訪問介面 (函式模板)
make_format_argsmake_wformat_args (C++20)(C++20)	建立引用所有格式化引數的型別擦除物件，可轉換為 format_args (函式模板)
輔助函式
format_kind (C++23)	為範圍選擇合適的 std::range_format (變數模板)
enable_nonlocking_formatter_optimization (C++23)	指示引數型別可以高效列印 (變數模板)

概要

namespace std {
  // class template basic_format_context
  template<class Out, class CharT> class basic_format_context;
  using format_context = basic_format_context</* unspecified */, char>;
  using wformat_context = basic_format_context</* unspecified */, wchar_t>;
 
  // class template basic_format_args
  template<class Context> class basic_format_args;
  using format_args = basic_format_args<format_context>;
  using wformat_args = basic_format_args<wformat_context>;
 
  // class template basic_format_string
  template<class CharT, class... Args>
    struct basic_format_string;
 
  template<class... Args>
    using format_string = basic_format_string<char, type_identity_t<Args>...>;
  template<class... Args>
    using wformat_string = basic_format_string<wchar_t, type_identity_t<Args>...>;
 
  // formatting functions
  template<class... Args>
    string format(format_string<Args...> fmt, Args&&... args);
  template<class... Args>
    wstring format(wformat_string<Args...> fmt, Args&&... args);
  template<class... Args>
    string format(const locale& loc, format_string<Args...> fmt, Args&&... args);
  template<class... Args>
    wstring format(const locale& loc, wformat_string<Args...> fmt, Args&&... args);
 
  string vformat(string_view fmt, format_args args);
  wstring vformat(wstring_view fmt, wformat_args args);
  string vformat(const locale& loc, string_view fmt, format_args args);
  wstring vformat(const locale& loc, wstring_view fmt, wformat_args args);
 
  template<class Out, class... Args>
    Out format_to(Out out, format_string<Args...> fmt, Args&&... args);
  template<class Out, class... Args>
    Out format_to(Out out, wformat_string<Args...> fmt, Args&&... args);
  template<class Out, class... Args>
    Out format_to(Out out, const locale& loc, format_string<Args...> fmt, Args&&... args);
  template<class Out, class... Args>
    Out format_to(Out out, const locale& loc, wformat_string<Args...> fmt, Args&&... args);
 
  template<class Out>
    Out vformat_to(Out out, string_view fmt, format_args args);
  template<class Out>
    Out vformat_to(Out out, wstring_view fmt, wformat_args args);
  template<class Out>
    Out vformat_to(Out out, const locale& loc, string_view fmt, format_args args);
  template<class Out>
    Out vformat_to(Out out, const locale& loc, wstring_view fmt, wformat_args args);
 
  template<class Out> struct format_to_n_result {
    Out out;
    iter_difference_t<Out> size;
  };
  template<class Out, class... Args>
    format_to_n_result<Out> format_to_n(Out out, iter_difference_t<Out> n,
                                        format_string<Args...> fmt, Args&&... args);
  template<class Out, class... Args>
    format_to_n_result<Out> format_to_n(Out out, iter_difference_t<Out> n,
                                        wformat_string<Args...> fmt, Args&&... args);
  template<class Out, class... Args>
    format_to_n_result<Out> format_to_n(Out out, iter_difference_t<Out> n,
                                        const locale& loc, format_string<Args...> fmt,
                                        Args&&... args);
  template<class Out, class... Args>
    format_to_n_result<Out> format_to_n(Out out, iter_difference_t<Out> n,
                                        const locale& loc, wformat_string<Args...> fmt,
                                        Args&&... args);
 
  template<class... Args>
    size_t formatted_size(format_string<Args...> fmt, Args&&... args);
  template<class... Args>
    size_t formatted_size(wformat_string<Args...> fmt, Args&&... args);
  template<class... Args>
    size_t formatted_size(const locale& loc, format_string<Args...> fmt, Args&&... args);
  template<class... Args>
    size_t formatted_size(const locale& loc, wformat_string<Args...> fmt, Args&&... args);
 
  // formatter
  template<class T, class CharT = char>
    struct formatter;
 
  // variable template enable_nonlocking_formatter_optimization
  template<class T>
    constexpr bool enable_nonlocking_formatter_optimization = false;
 
  // concept formattable
  template<class T, class CharT>
    concept formattable = /* see description */;
 
  template<class R, class CharT>
    concept __const_formattable_range =                               // exposition only
      ranges::input_range<const R> &&
      formattable<ranges::range_reference_t<const R>, CharT>;
 
  template<class R, class CharT>
    using __fmt_maybe_const =                                         // exposition only
      conditional_t<__const_formattable_range<R, CharT>, const R, R>;
 
  // class template basic_format_parse_context
  template<class CharT> class basic_format_parse_context;
  using format_parse_context = basic_format_parse_context<char>;
  using wformat_parse_context = basic_format_parse_context<wchar_t>;
 
  // formatting of ranges
  // variable template format_kind
  enum class range_format {
    disabled,
    map,
    set,
    sequence,
    string,
    debug_string
  };
 
  template<class R>
    constexpr /* unspecified */ format_kind = /* unspecified */;
 
  template<ranges::input_range R>
      requires same_as<R, remove_cvref_t<R>>
    constexpr range_format format_kind<R> = /* see description */;
 
  // class template range_formatter
  template<class T, class CharT = char>
    requires same_as<remove_cvref_t<T>, T> && formattable<T, CharT>
  class range_formatter;
 
  // class template range-default-formatter
  template<range_format K, ranges::input_range R, class CharT>
    struct __range_default_formatter;                                 // exposition only
 
  // specializations for maps, sets, and strings
  template<ranges::input_range R, class CharT>
    requires (format_kind<R> != range_format::disabled) &&
             formattable<ranges::range_reference_t<R>, CharT>
  struct formatter<R, CharT> : __range_default_formatter<format_kind<R>, R, CharT> { };
 
  // arguments
  // class template basic_format_arg
  template<class Context> class basic_format_arg;
 
  template<class Visitor, class Context>
    decltype(auto) visit_format_arg(Visitor&& vis, basic_format_arg<Context> arg);
 
  // class template format-arg-store
  template<class Context, class... Args> class __format_arg_store;    // exposition only
 
  template<class Context = format_context, class... Args>
    __format_arg_store<Context, Args...>
      make_format_args(Args&&... fmt_args);
  template<class... Args>
    __format_arg_store<wformat_context, Args...>
      make_wformat_args(Args&&... args);
 
  // class format_error
  class format_error;
}

類模板 std::basic_format_string

namespace std {
  template<class CharT, class... Args>
  struct basic_format_string {
  private:
    basic_string_view<CharT> str;         // exposition only
 
  public:
    template<class T> consteval basic_format_string(const T& s);
 
    constexpr basic_string_view<CharT> get() const noexcept { return str; }
  };
}

概念 std::formattable

template<class T, class CharT>
  concept formattable =
    semiregular<formatter<remove_cvref_t<T>, CharT>> &&
    requires(formatter<remove_cvref_t<T>, CharT> f,
             const formatter<remove_cvref_t<T>, CharT> cf,
             T t,
             basic_format_context<__fmt_iter_for<CharT>, CharT> fc,
             basic_format_parse_context<CharT> pc) {
        { f.parse(pc) } -> same_as<basic_format_parse_context<CharT>::iterator>;
        { cf.format(t, fc) } -> same_as<__fmt_iter_for<CharT>>;
    };

類模板 std::basic_format_parse_context

namespace std {
  template<class CharT>
  class basic_format_parse_context {
  public:
    using char_type = CharT;
    using const_iterator = typename basic_string_view<CharT>::const_iterator;
    using iterator = const_iterator;
 
  private:
    iterator begin_;                                    // exposition only
    iterator end_;                                      // exposition only
    enum indexing { unknown, manual, automatic };       // exposition only
    indexing indexing_;                                 // exposition only
    size_t next_arg_id_;                                // exposition only
    size_t num_args_;                                   // exposition only
 
  public:
    constexpr explicit basic_format_parse_context(basic_string_view<CharT> fmt,
                                                  size_t num_args = 0) noexcept;
    basic_format_parse_context(const basic_format_parse_context&) = delete;
    basic_format_parse_context& operator=(const basic_format_parse_context&) = delete;
 
    constexpr const_iterator begin() const noexcept;
    constexpr const_iterator end() const noexcept;
    constexpr void advance_to(const_iterator it);
 
    constexpr size_t next_arg_id();
    constexpr void check_arg_id(size_t id);
 
    template<class... Ts>
    constexpr void check_dynamic_spec(size_t id) noexcept;
    constexpr void check_dynamic_spec_integral(size_t id) noexcept;
    constexpr void check_dynamic_spec_string(size_t id) noexcept;
  };
}

類模板 std::basic_format_context

namespace std {
  template<class Out, class CharT>
  class basic_format_context {
    basic_format_args<basic_format_context> args_;      // exposition only
    Out out_;                                           // exposition only
 
    basic_format_context(const basic_format_context&) = delete;
    basic_format_context& operator=(const basic_format_context&) = delete;
 
  public:
    using iterator = Out;
    using char_type = CharT;
    template<class T> using formatter_type = formatter<T, CharT>;
 
    basic_format_arg<basic_format_context> arg(size_t id) const noexcept;
    std::locale locale();
 
    iterator out();
    void advance_to(iterator it);
  };
}

變數模板 std::format_kind

template<ranges::input_range R>
    requires same_as<R, remove_cvref_t<R>>
  constexpr range_format format_kind<R> = /* see description */;

類模板 std::range_formatter

namespace std {
  template<class T, class CharT = char>
    requires same_as<remove_cvref_t<T>, T> && formattable<T, CharT>
  class range_formatter {
    formatter<T, CharT> underlying_;                        // exposition only
    basic_string_view<CharT> separator_ =                   // exposition only
      __STATICALLY_WIDEN<CharT>(", ");
    basic_string_view<CharT> __opening_bracket_ =           // exposition only
      __STATICALLY_WIDEN<CharT>("[");
    basic_string_view<CharT> __closing_bracket_ =           // exposition only
      __STATICALLY_WIDEN<CharT>("]");
 
  public:
    constexpr void set_separator(basic_string_view<CharT> sep);
    constexpr void set_brackets(basic_string_view<CharT> opening,
                                basic_string_view<CharT> closing);
    constexpr formatter<T, CharT>& underlying() { return underlying_; }
    constexpr const formatter<T, CharT>& underlying() const { return underlying_; }
 
    template<class ParseContext>
      constexpr typename ParseContext::iterator
        parse(ParseContext& ctx);
 
    template<ranges::input_range R, class FormatContext>
        requires formattable<ranges::range_reference_t<R>, CharT> &&
                 same_as<remove_cvref_t<ranges::range_reference_t<R>>, T>
      typename FormatContext::iterator
        format(R&& r, FormatContext& ctx) const;
  };
}

類模板 __range_default_formatter

namespace std {
  template<ranges::input_range R, class CharT>
  struct __range_default_formatter<range_format::sequence, R, CharT> {
  private:
    using __maybe_const_r = __fmt_maybe_const<R, CharT>;
    range_formatter<remove_cvref_t<ranges::range_reference_t<__maybe_const_r>>,
                    CharT> underlying_;       // exposition only
 
  public:
    constexpr void set_separator(basic_string_view<CharT> sep);
    constexpr void set_brackets(basic_string_view<CharT> opening,
                                basic_string_view<CharT> closing);
 
    template<class ParseContext>
      constexpr typename ParseContext::iterator
        parse(ParseContext& ctx);
 
    template<class FormatContext>
      typename FormatContext::iterator
        format(__maybe_const_r& elems, FormatContext& ctx) const;
  };
}

針對 map 的 __range_default_formatter 特化

namespace std {
  template<ranges::input_range R, class CharT>
  struct __range_default_formatter<range_format::map, R, CharT> {
  private:
    using __maybe_const_map = __fmt_maybe_const<R, CharT>;          // exposition only
    using __element_type =                                          // exposition only
      remove_cvref_t<ranges::range_reference_t<__maybe_const_map>>;
    range_formatter<__element_type, CharT> underlying_;             // exposition only
  public:
    constexpr __range_default_formatter();
 
    template<class ParseContext>
      constexpr typename ParseContext::iterator
        parse(ParseContext& ctx);
 
    template<class FormatContext>
      typename FormatContext::iterator
        format(__maybe_const_map& r, FormatContext& ctx) const;
  };
}

針對 set 的 __range_default_formatter 特化

namespace std {
  template<ranges::input_range R, class CharT>
  struct __range_default_formatter<range_format::set, R, CharT> {
  private:
    using __maybe_const_set = __fmt_maybe_const<R, CharT>;          // exposition only
    range_formatter<remove_cvref_t<ranges::range_reference_t<__maybe_const_set>>,
                    CharT> underlying_;                             // exposition only
  public:
    constexpr __range_default_formatter();
 
    template<class ParseContext>
      constexpr typename ParseContext::iterator
        parse(ParseContext& ctx);
 
    template<class FormatContext>
      typename FormatContext::iterator
        format(__maybe_const_set& r, FormatContext& ctx) const;
  };
}

針對 string 的 __range_default_formatter 特化

namespace std {
  template<range_format K, ranges::input_range R, class CharT>
    requires (K == range_format::string || K == range_format::debug_string)
  struct __range_default_formatter<K, R, CharT> {
  private:
    formatter<basic_string<CharT>, CharT> underlying_;              // exposition only
 
  public:
    template<class ParseContext>
      constexpr typename ParseContext::iterator
        parse(ParseContext& ctx);
 
    template<class FormatContext>
      typename FormatContext::iterator
        format(/* see description */& str, FormatContext& ctx) const;
  };
}

類模板 std::basic_format_arg

namespace std {
  template<class Context>
  class basic_format_arg {
  public:
    class handle;
 
  private:
    using char_type = typename Context::char_type;                     // exposition only
 
    variant<monostate, bool, char_type,
            int, unsigned int, long long int, unsigned long long int,
            float, double, long double,
            const char_type*, basic_string_view<char_type>,
            const void*, handle> value;                                // exposition only
 
    template<class T> explicit basic_format_arg(T&& v) noexcept;       // exposition only
    explicit basic_format_arg(float n) noexcept;                       // exposition only
    explicit basic_format_arg(double n) noexcept;                      // exposition only
    explicit basic_format_arg(long double n) noexcept;                 // exposition only
    explicit basic_format_arg(const char_type* s);                     // exposition only
 
    template<class traits>
      explicit basic_format_arg(
        basic_string_view<char_type, traits> s) noexcept;              // exposition only
 
    template<class traits, class Allocator>
      explicit basic_format_arg(
        const basic_string<char_type, traits, Allocator>& s) noexcept; // exposition only
 
    explicit basic_format_arg(nullptr_t) noexcept;                     // exposition only
 
    template<class T>
      explicit basic_format_arg(T* p) noexcept;                        // exposition only
 
  public:
    basic_format_arg() noexcept;
 
    explicit operator bool() const noexcept;
 
    template<class Visitor>
      decltype(auto) visit(this basic_format_arg arg, Visitor&& vis);
    template<class R, class Visitor>
      R visit(this basic_format_arg arg, Visitor&& vis);
  };
}

類 std::basic_format_arg::handle

namespace std {
  template<class Context>
  class basic_format_arg<Context>::handle {
    const void* ptr_;                                           // exposition only
    void (*format_)(basic_format_parse_context<char_type>&,
                    Context&, const void*);                     // exposition only
 
    template<class T> explicit handle(T&& val) noexcept;        // exposition only
 
    friend class basic_format_arg<Context>;                     // exposition only
 
  public:
    void format(basic_format_parse_context<char_type>&, Context& ctx) const;
  };
}

類模板 __format_arg_store

namespace std {
  template<class Context, class... Args>
  class __format_arg_store {                                    // exposition only
    array<basic_format_arg<Context>, sizeof...(Args)> args;     // exposition only
  };
}

類模板 std::basic_format_args

namespace std {
  template<class Context>
  class basic_format_args {
    size_t size_;                               // exposition only
    const basic_format_arg<Context>* data_;     // exposition only
 
  public:
    template<class... Args>
      basic_format_args(const __format_arg_store<Context, Args...>& store) noexcept;
 
    basic_format_arg<Context> get(size_t i) const noexcept;
  };
}

元組格式化器

namespace std {
  template<class CharT, formattable<CharT>... Ts>
  struct formatter<__pair_or_tuple<Ts...>, CharT> {
  private:
    tuple<formatter<remove_cvref_t<Ts>, CharT>...> underlying_;     // exposition only
    basic_string_view<CharT> separator_ =                           // exposition only
      __STATICALLY_WIDEN<CharT>(", ");
    basic_string_view<CharT> opening_bracket_ =                     // exposition only
      __STATICALLY_WIDEN<CharT>("(");
    basic_string_view<CharT> closing_bracket_ =                     // exposition only
      __STATICALLY_WIDEN<CharT>(")");
 
  public:
    constexpr void set_separator(basic_string_view<CharT> sep);
    constexpr void set_brackets(basic_string_view<CharT> opening,
                                basic_string_view<CharT> closing);
 
    template<class ParseContext>
      constexpr typename ParseContext::iterator
        parse(ParseContext& ctx);
 
    template<class FormatContext>
      typename FormatContext::iterator
        format(/* see description */& elems, FormatContext& ctx) const;
  };
}

類 std::format_error

namespace std {
  class format_error : public runtime_error {
  public:
    explicit format_error(const string& what_arg);
    explicit format_error(const char* what_arg);
  };
}