function::user_ulong_error - Linux


function::user_ulong_error generates a user-defined error code with an unsigned long field.


function::user_ulong_error(error_code_or_condition, domain, number, msg, ulong_code)


  • error_code_or_condition: The error code (e.g., std::errc::invalid_argument) or a system_error condition.
  • domain: The error domain.
  • number: The error number within the specified error domain.
  • msg: The human-readable error message.
  • ulong_code: The unsigned long error code to be associated with the generated error.


Simple Example:

auto ec = function::user_ulong_error(std::errc::invalid_argument, std::generic_category(), 42, "Invalid arguments", 123456789);

Complex Example with Macros:

#include <concepts/concepts.hpp>
#include <functional/error.hpp>

namespace fs = std::filesystem;

namespace custom {
    constexpr auto custom_domain = std::error_domain("custom.domain");

    namespace error {
        constexpr auto invalid_path = MAKE_USER_ULONG_ERROR_CODE(custom_domain, 1, "Invalid path");
    } // namespace error
} // namespace custom

int main() {
    const fs::path invalid_path("/non/existing/path");

    try {
    } catch (const std::exception& e) {
        if (auto ec = concepts::unexpected_error(e)) {
            if (ec == custom::error::invalid_path) {
                std::cerr << "Invalid path: " << ec.message() << std::endl;
                return ec.value();

Common Issues

  • Ensure that the error domain is unique to avoid conflicts with other domains.
  • Use descriptive error messages to aid in debugging.
  • Check for the existence of the unsigned long error code field in the error handling code.


  • Combine with concepts::unexpected_error() to extract error codes from exceptions.
  • Integrate with custom::error_code_traits for advanced error handling and customization.

Related Commands