What is the purpose of a unary "+" before a call to std::numeric_limits<unsigned char> members?

Question

I saw this example in cppreference's documentation for std::numeric_limits

#include <limits>
#include <iostream>

int main() 
{
    std::cout << "type\tlowest()\tmin()\t\tmax()\n\n";

    std::cout << "uchar\t"
              << +std::numeric_limits<unsigned char>::lowest() << '\t' << '\t'
              << +std::numeric_limits<unsigned char>::min() << '\t' << '\t'
              << +std::numeric_limits<unsigned char>::max() << '\n';
    std::cout << "int\t"
              << std::numeric_limits<int>::lowest() << '\t'
              << std::numeric_limits<int>::min() << '\t'
              << std::numeric_limits<int>::max() << '\n';
    std::cout << "float\t"
              << std::numeric_limits<float>::lowest() << '\t'
              << std::numeric_limits<float>::min() << '\t'
              << std::numeric_limits<float>::max() << '\n';
    std::cout << "double\t"
              << std::numeric_limits<double>::lowest() << '\t'
              << std::numeric_limits<double>::min() << '\t'
              << std::numeric_limits<double>::max() << '\n';
}

I don't understand the "+" operator in

<< +std::numeric_limits<unsigned char>::lowest()

I have tested it, replaced it with "-", and that also worked. What is the use of such a "+" operator?

Answer 1

The output operator << when being passed a char (signed or unsigned) will write it as a character.

Those function will return values of type unsigned char. And as noted above that will print the characters those values represent in the current encoding, not their integer values.

The + operator converts the unsigned char returned by those functions to an int through integer promotion. Which means the integer values will be printed instead.

An expression like +std::numeric_limits<unsigned char>::lowest() is essentially equal to static_cast<int>(std::numeric_limits<unsigned char>::lowest()).