Difference between revisions of "cpp/utility/to chars result"
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{{tt|std::to_chars_result}} is the return type of {{ltt std|cpp/utility/to_chars}}. It has no base classes, and only has the following members. | {{tt|std::to_chars_result}} is the return type of {{ltt std|cpp/utility/to_chars}}. It has no base classes, and only has the following members. | ||
| − | === | + | ===Data members=== |
{{dsc begin}} | {{dsc begin}} | ||
| − | {{dsc hitem| | + | {{dsc hitem|Name|Type}} |
{{dsc|{{tt|ptr}}|{{c/core|const char*}}}} | {{dsc|{{tt|ptr}}|{{c/core|const char*}}}} | ||
{{dsc|{{tt|ec}}|{{lc|std::errc}}}} | {{dsc|{{tt|ec}}|{{lc|std::errc}}}} | ||
Revision as of 02:21, 6 September 2023
| 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 |
Data members
| Name | Type |
ptr
|
const char* |
ec
|
std::errc |
Member and friend functions
operator==(std::to_chars_result)
| friend bool operator==( const to_chars_result&, const to_chars_result& ) = default; |
(since C++20) | |
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{}.
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 |
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
See also
| (C++17) |
converts an integer or floating-point value to a character sequence (function) |
