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C++17 in Detail: A Deep Dive

Examples

Explore how to convert strings to numbers in C++17 using from_chars, covering integral and floating-point types. Understand error handling and format options to improve performance and reliability in string conversions.

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Here are two examples of how to convert a string into a number using from_chars. The first one will convert into int and the second one converts into a floating-point number.

Integral types

C++ 17
#include <iostream>
#include <charconv> // from_chars, to_chars
#include <string>
int main()
{
    const std::string str { "12345678901234" };
    int value = 0;
    const auto res = std::from_chars(str.data(),
                                     str.data() + str.size(),
                                     value);
    if (res.ec == std::errc())
    {
        std::cout << "value: " << value << ", distance: " << res.ptr - str.data() << '\n';
    }
    else if (res.ec == std::errc::invalid_argument)
    {
        std::cout << "invalid argument!\n";
    }
    else if (res.ec == std::errc::result_out_of_range)
    {
        std::cout << "out of range! res.ptr distance: " << res.ptr - str.data() << '\n';
    }
}

The example is straightforward, it passes a string str into from_chars and then displays the result with additional information if possible.

Below you can find an output for various str value.

str value Output
...