All Error-Code Facilities

Core types from <system_error>

• std::error_code
• std::error_condition
• std::error_category
• std::system_error
• std::errc

Factory and conversion helpers

• std::make_error_code
• std::make_error_condition
• implicit conversions from enums with enabled traits

Filesystem integration

• std::filesystem::filesystem_error
• non-throwing overloads that accept std::error_code&

Typical API style

• throw-on-failure overloads for convenience
• error_code out-parameter overloads for non-throwing control flow

Practical rules

• Use std::error_code when local branching is expected and exceptions would be noise.
• Use exceptions when failure should propagate automatically and callers are not expected to inspect codes immediately.
• Keep domain-specific error enums mapped through a clear error_category.

Small worked example

#include <filesystem>
#include <string_view>
#include <system_error>

std::error_code prepare_output_directory(std::string_view name) {
	std::error_code ec;
	std::filesystem::path dir{"output"};
	dir /= name;
	std::filesystem::create_directories(dir, ec);
	return ec;
}

int main() {
	if (std::error_code ec = prepare_output_directory("reports")) {
		return ec == std::errc::permission_denied ? 2 : 1;
	}
	return 0;
}

This is the common error_code shape: do a non-throwing operation, branch locally, and keep the caller in charge of how much error detail matters.

Decision habit

• choose error_code when failure is expected and the caller can recover immediately
• choose exceptions when the right behavior is usually to stop the current operation and unwind
• compare categories and standard conditions when you need portability, not raw integer values

Related pages

• Standard exceptions and errors
• Header reference: <filesystem>
• Header reference: <expected>