simple_enum

std::format Support for enumerations

Overview

Starting from C++20, std::format introduces a new, type-safe way to perform string formatting. The simple_enum library extends std::format support to enumerations through a custom std::formatter specialization, enabling seamless string formatting of enum values.

Availability

This feature is available under the following conditions:

• The C++20 standard is being used, or the __cpp_lib_format feature test macro is defined, indicating the availability of std::format.

Implementation

The custom std::formatter specialization for enumerations is provided through the simple_enum/std_format.hpp header.

• The formatter is defined only for enumerations satisfying simple_enum::bounded_enum (first/last enumerators, simple_enum::info specialization or adl_enum_bounds). It is not defined for other enumerations, so standard enumerations like std::byte or std::errc are not affected.
• The format spec is the same as for std::string_view (fill, align, width, precision), e.g. std::format("{:>10}", value).
• A value without a name is formatted as its underlying integer value, e.g. static_cast<my_enum>(42) gives 42.

Usage

Include the simple_enum/std_format.hpp header to enable std::format support for your enumerations:

#include <simple_enum/std_format.hpp>

Example Code

#include <iostream>
#include <format>
#include "simple_enum/std_format.hpp"  // Include custom formatter support

enum class lorem_ipsum_short { eu, occaecat, dolore, first = eu, last = dolore };

int main() {
    // Use std::format to format an enum value directly
    std::cout << std::format("{}\n", lorem_ipsum_short::eu);  // Outputs: eu
    std::cout << std::format("[{:>8}]\n", lorem_ipsum_short::dolore);  // Outputs: [  dolore]
    std::cout << std::format("{}\n", static_cast<lorem_ipsum_short>(42));  // Outputs: 42
}

This code snippet demonstrates how to format an enumeration value to a string using std::format, provided that the enum satisfies simple_enum::bounded_enum and simple_enum/std_format.hpp is included.

Requirements

• Compiler and library support for C++20 and specifically for the std::format feature.

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