Standard library header <format> (C++20)

 

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Standard Library headers

Note: a slash '/' in a revision mark means that the header was deprecated and/or removed.

Language Support
<cstddef> <cstdlib> <version> (C++20) <limits> <climits>	<cfloat> <cstdint> (C++11) <new> <typeinfo>	<source_location> (C++20) <exception> <initializer_list> (C++11)   <compare> (C++20)	<coroutine> (C++20) <csignal> <csetjmp> <cstdarg>
Concepts
<concepts> (C++20)
Diagnostics
<stdexcept>	<cassert>	<cerrno>	<system_error> (C++11)
General utilities
<utility> <memory> <memory_resource> (C++17) <scoped_allocator> (C++11)   <expected> (C++23)	<bitset> <tuple> (C++11) <optional> (C++17) <any> (C++17)	<variant> (C++17) <type_traits> (C++11) <ratio> (C++11) <chrono> (C++11)	<typeindex> (C++11) <functional> <stacktrace> (C++23) <ctime>
Strings
<string> <string_view> (C++17) <cstring>	<charconv> (C++17) <format> (C++20)	<cctype> <cwctype>	<cwchar> <cuchar> (C++11)
Localization
<locale> <clocale>	<codecvt> (C++11/17)
Containers
<span> (C++20) <array> (C++11) <vector>	<deque> <forward_list> (C++11) <list>	<map> <set> <queue>	<unordered_map> (C++11) <unordered_set> (C++11) <stack>
Iterators
<iterator>
Ranges
<ranges> (C++20)
Algorithms
<algorithm>	<execution> (C++17)
Numerics
<complex> <random> (C++11)	<valarray> <numeric>	<bit> (C++20) <numbers> (C++20)	<cfenv> (C++11) <cmath>
Input/Output
<iosfwd> <ios> <iomanip> <streambuf>	<istream> <ostream> <iostream>	<syncstream> (C++20) <spanstream> (C++23) <sstream> <fstream>	<cstdio> <cinttypes> (C++11) <strstream> (C++98/)
Regular expressions
<regex> (C++11)
Filesystem support
<filesystem> (C++17)
Thread support
<thread> (C++11) <atomic> (C++11) <mutex> (C++11)	<shared_mutex> (C++14) <condition_variable> (C++11)   <future> (C++11)	<stop_token> (C++20) <semaphore> (C++20)	<latch> (C++20) <barrier> (C++20)
C compatibility
<cstdbool> (C++11/17/20) <ccomplex> (C++11/17/20)	<ctgmath> (C++11/17/20) <cstdalign> (C++11/17/20)	<ciso646> (until C++20) <stdatomic.h>

 

This header is part of the format library.

Classes
formatter (C++20)	class template that defines formatting rules for a given type (class template)
basic_format_parse_contextformat_parse_contextwformat_parse_context (C++20)(C++20)(C++20)	formatting string parser state (class template)
basic_format_contextformat_contextwformat_context (C++20)(C++20)(C++20)	formatting state, including all formatting arguments and the output iterator (class template)
basic_format_arg (C++20)	class template that provides access to a formatting argument for user-defined formatters (class template)
basic_format_argsformat_argswformat_args (C++20)(C++20)(C++20)	class that provides access to all formatting arguments (class template)
format_error (C++20)	exception type thrown on formatting errors (class)
Functions
format (C++20)	stores formatted representation of the arguments in a new string (function template)
format_to (C++20)	writes out formatted representation of its arguments through an output iterator (function template)
format_to_n (C++20)	writes out formatted representation of its arguments through an output iterator, not exceeding specified size (function template)
formatted_size (C++20)	determines the number of characters necessary to store the formatted representation of its arguments (function template)
vformat (C++20)	non-template variant of std::format using type-erased argument representation (function)
vformat_to (C++20)	non-template variant of std::format_to using type-erased argument representation (function template)
visit_format_arg (C++20)	argument visitation interface for user-defined formatters (function template)
make_format_argsmake_wformat_args (C++20)(C++20)	creates a type-erased object referencing all formatting arguments, convertible to format_args (function template)

Synopsis

namespace std {
  // basic format string
  template<class charT, class... Args> struct /*basic-format-string*/; // exposition only
 
  template<class... Args>
    using /*format-string*/ 
    = /*basic-format-string*/<char, type_identity_t<Args>...>; // exposition only
  template<class... Args>
    using /*wformat-string*/ 
    = /*basic-format-string*/<wchar_t, type_identity_t<Args>...>; // exposition only
 
  // 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;
 
  // 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>;
 
  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>;
 
  // arguments
  // class template basic_format_arg
  template<class Context> class basic_format_arg;
 
  template<class Visitor, class Context>
    /* see description */ visit_format_arg(Visitor&& vis, basic_format_arg<Context> arg);
 
  // class template format-arg-store
  template<class Context, class... Args> struct /*format-arg-store*/;  // exposition only
 
  template<class Context = format_context, class... Args>
    /*format-arg-store*/<Context, Args...>
      make_format_args(Args&&... args);
  template<class... Args>
    /*format-arg-store*/<wformat_context, Args...>
      make_wformat_args(Args&&... args);
 
  // 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 format_error
  class format_error;
}

Class template basic-format-string

namespace std {
  template<class charT, class... Args>
  struct /*basic-format-string*/ {  // exposition only
  private:
    basic_string_view<charT> str_;  // exposition only
 
  public:
    template<class T> consteval /*basic-format-string*/(const T& s);
  };
}

Class template 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);
  };
}

Class template 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
 
  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;
    std::locale locale();
 
    iterator out();
    void advance_to(iterator it);
  };
}

Class template 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(const T* p) noexcept;                  // exposition only
 
  public:
    basic_format_arg() noexcept;
 
    explicit operator bool() const noexcept;
  };
}

Class 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;
  };
}

Class template format-arg-store

namespace std {
  template<class Context, class... Args>
  struct /*format-arg-store*/ {      // exposition only
    array<basic_format_arg<Context>, sizeof...(Args)> args;
  };
}

Class template 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:
    basic_format_args() noexcept;
 
    template<class... Args>
      basic_format_args(const /*format-arg-store*/<Context, Args...>& store) noexcept;
 
    basic_format_arg<Context> get(size_t i) const noexcept;
  };
}

Class 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);
  };
}