C++ Basics: Initialize a Maximum for Negative Data

Use numeric_limits::lowest when a floating-point maximum accumulator must handle negative values.

Prepare a scratch directory

Tested on Linux x86_64 with GCC 14.2.0. Install a C++20-capable compiler and standard-library development headers, with g++ on PATH. You also need Bash, a text editor, and the mktemp, rm, and rmdir utilities. No third-party library is required.

Keep the same terminal open. Stop if setup fails, before saving the source:

start_directory="$PWD"
work_directory="$(mktemp -d)" || exit 1
cd -- "$work_directory" || exit 1

Run the example

Save this as numeric-limits-lowest-negative-data-demo.cpp:

#include <algorithm>
#include <array>
#include <iostream>
#include <limits>

int main()
{
    constexpr std::array<double, 3> readings{-8.0, -3.0, -12.0};
    double highest = std::numeric_limits<double>::lowest();
    for (double value : readings) {
        highest = std::max(highest, value);
    }
    std::cout << "highest: " << highest << '\n';
    std::cout << std::boolalpha
              << "min is positive: "
              << (std::numeric_limits<double>::min() > 0.0) << '\n';
}

Compile and run it. The program runs only after compilation succeeds:

g++ -std=c++20 -Wall -Wextra -Werror -pedantic numeric-limits-lowest-negative-data-demo.cpp -o numeric-limits-lowest-negative-data-demo &&
./numeric-limits-lowest-negative-data-demo

Observed output:

highest: -3
min is positive: true

Read the result

The maximum reading is -3. For double on this platform, min() is a small positive normalized value, so it is the wrong starting point for this loop. lowest() supplies the lowest finite value.

Apply it carefully

This example assumes a nonempty collection of finite readings. For potentially empty input, represent absence explicitly or test emptiness before computing a result. Decide how to handle NaN and infinities separately; lowest() is a finite bound, not negative infinity.

The C++ working draft describes the relevant rules. This example builds in C++20 mode; the current working draft also documents later additions.

Clean up

Remove only the source and executable created here, then return to the starting directory:

rm -- numeric-limits-lowest-negative-data-demo.cpp numeric-limits-lowest-negative-data-demo
cd -- "$start_directory" || exit 1
rmdir -- "$work_directory"
unset start_directory work_directory

If the directory is not empty, inspect its remaining contents before removing anything else.

Acknowledgements

This post was created with assistance from AI.