std::to_chars_result
From cppreference.com
| 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.
Data members
| Member name | Definition |
ptr |
a pointer of type char* (public member object) |
ec |
an error code of type std::errc (public member object) |
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) |