std::to_chars_result
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C++
Feature test macros (C++20)
Concepts library (C++20)
Metaprogramming library (C++11)
Ranges library (C++20)
Filesystem library (C++17)
Concurrency support library (C++11)
Execution control library (C++26)
Text processing library
Regular expressions library (C++11)
Formatting library (C++20)
Defined in header
<charconv>
struct to_chars_result;
(since C++17)
std::to_chars_result is the return type of std::to_chars. It has no base classes, and only has the following members.
Contents
[edit] Data members
Member name
Definition
ptr
(public member object)
[edit] Member and friend functions
operator==(std::to_chars_result)
friend bool operator==( const to_chars_result&,
const to_chars_result& ) = default;
(since C++20)
const to_chars_result& ) = default;
Compares the two arguments using default comparisons (which uses operator== to compare ptr and ec respectively).
This function is not visible to ordinary unqualified or qualified lookup, and can only be found by argument-dependent lookup when std::to_chars_result is an associated class of the arguments.
The != operator is synthesized from operator==.
operator bool
constexpr explicit operator bool() const noexcept;
(since C++26)
Checks whether the conversion is successful. Returns ec == std::errc {}.
[edit] Notes
| Feature-test macro | Value | Std | Feature |
|---|---|---|---|
__cpp_lib_to_chars |
201611L |
(C++17) | Elementary string conversions (std::to_chars, std::from_chars) |
202306L |
(C++26) | Testing for success or failure of <charconv> functions |
[edit] Example
Run this code
#include <array> #include <charconv> #include <iostream> #include <string_view> #include <system_error> void show_to_chars(auto... format_args) { std::array <char, 10> str; #if __cpp_lib_to_chars >= 202306L and __cpp_structured_bindings >= 202406L // use C++26 structured bindings declaration as condition (P0963) // and C++26 to_chars_result::operator bool() for error checking (P2497) if (auto [ptr, ec] = std::to_chars (str.data(), str.data() + str.size(), format_args...)) std::cout << std::string_view (str.data(), ptr) << '\n'; else std::cout << std::make_error_code (ec).message() << '\n'; #elif __cpp_lib_to_chars >= 202306L // use C++26 to_chars_result::operator bool() for error checking (P2497) if (auto result = std::to_chars (str.data(), str.data() + str.size(), format_args...)) std::cout << std::string_view (str.data(), result.ptr) << '\n'; else std::cout << std::make_error_code (result.ec).message() << '\n'; #else // fallback to C++17 if-with-initializer and structured bindings if (auto [ptr, ec] = std::to_chars (str.data(), str.data() + str.size(), format_args...); ec == std::errc ()) std::cout << std::string_view (str.data(), ptr - str.data()) << '\n'; else std::cout << std::make_error_code (ec).message() << '\n'; #endif } int main() { show_to_chars(42); show_to_chars(+3.14159F); show_to_chars(-3.14159, std::chars_format::fixed); show_to_chars(-3.14159, std::chars_format::scientific, 3); show_to_chars(3.1415926535, std::chars_format::fixed, 10); }
Possible output:
42 3.14159 -3.14159 -3.142e+00 Value too large for defined data type