std::from_chars_result - cppreference.com (original) (raw)

| | | | | --------------------------- | | ------------- | | struct from_chars_result; | | (since C++17) |

std::from_chars_result is the return type of std::from_chars. It has no base classes, and only has the following members.

Contents

• 1 Data members
• 2 Member and friend functions
• 3 operator==(std::from_chars_result)
• 4 operator bool
  • 4.1 Notes
  • 4.2 Example
  • 4.3 See also

[edit] Data members

[edit] Member and friend functions

operator==(std::from_chars_result)

| friend bool operator==( const from_chars_result&, const from_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::from_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

[edit] Example

#include #include #include #include #include #include #include   int main() { for (std::string_view const str : {"1234", "15 foo", "bar", " 42", "5000000000"}) { std::cout << "String: " << std::quoted(str) << ". "; int result{}; auto [ptr, ec] = std::from_chars(str.data(), str.data() + str.size(), result);   if (ec == std::errc()) std::cout << "Result: " << result << ", ptr -> " << std::quoted(ptr) << '\n'; else if (ec == std::errc::invalid_argument) std::cout << "This is not a number.\n"; else if (ec == std::errc::result_out_of_range) std::cout << "This number is larger than an int.\n"; }   // C++23's constexpr from_char demo / C++26's operator bool() demo: auto to_int = s) -> std::optional { int value{}; #if __cpp_lib_to_chars >= 202306L if (std::from_chars(s.data(), s.data() + s.size(), value)) #else if (std::from_chars(s.data(), s.data() + s.size(), value).ec == std::errc{}) #endif return value; else return std::nullopt; };   assert(to_int("42") == 42); assert(to_int("foo") == std::nullopt); #if __cpp_lib_constexpr_charconv and __cpp_lib_optional >= 202106 static_assert(to_int("42") == 42); static_assert(to_int("foo") == std::nullopt); #endif }

Output:

String: "1234". Result: 1234, ptr -> "" String: "15 foo". Result: 15, ptr -> " foo" String: "bar". This is not a number. String: " 42". This is not a number. String: "5000000000". This number is larger than an int.

[edit] See also

| | converts a character sequence to an integer or floating-point value (function) [edit] | | --------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------- |