1

The following program

#include <charconv>
#include <string>
#include <iostream>

int main() {
    std::string s = "0X1.BC70A3D70A3D7P+6";
    std::cout << "strtod: " << std::strtod(s.c_str(), nullptr) << std::endl;
    double d = 42;
    std::from_chars(s.data(), s.data() + s.size(), d, std::chars_format::general);
    std::cout << "from_chars: " << d << std::endl;
}

prints

strtod: 111.11
from_chars: 0

when compiled with GCC on Linux. Can std::from_chars not handle hexadecimal floating-point numbers?

Improve this question
19
  • 1
    As per std::from_chars it doesn't handle the leading 0X. Commented Nov 15, 2024 at 19:00
  • 1
    @Eljay only if fmt is std::chars_format::hex if I understood that documentation correctly Commented Nov 15, 2024 at 19:01
  • if fmt is std::chars_format::hex, the prefix "0x" or "0X" is not permitted (the string "0x123" parses as the value "0" with unparsed remainder "x123") Commented Nov 15, 2024 at 19:04
  • 1
    @AhmedAEK found it. Looks like cppref and the standard agree. Commented Nov 15, 2024 at 19:30
  • 2
    The important part is eel.is/c++draft/charconv#to.chars-3 -- the std::chars_format::general expects the string to be in %g format. That's not a hex format. Commented Nov 15, 2024 at 19:34
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