palindrome.cpp

#include <algorithm>
#include <print>
#include <span>
#include <string_view>

// Separate this out into a function to make it easier to test.
bool is_palindrome(std::string_view s) {
	// Avoids manual pointer manipulation, still does n/2 checks.
	// Note: integer division floors, but this is correct since given an
	// odd-length string, middle char will always equal itself.
	return std::equal(s.begin(), s.begin() + s.size() / 2, s.rbegin());
}

int main(int argc, char *argv[]) {
	// std::span wraps a raw array (pointer + length) into something we can
	// iterate safely. Note: .subspan(1) skips argv[0] (the program name).
	auto args = std::span(argv, argc).subspan(1);

	// Bail out early if no args provided.
	if (args.empty()) {
		// Use modern std::println instead of std::cout
		std::println("Usage: ./palindrome arg1 [arg2 [arg3 ...]]");
		// EXIT_FAILURE expands to a platform appropriate failure return
		// code (usually 1).
		return EXIT_FAILURE;
	}

	// Iterate over args, each char* implicitly converts to a string_view
	// called arg (no copy, just a view). Print out whether each argument is
	// a palindrome.
	for (std::string_view arg : args) {
		if (is_palindrome(arg)) {
			std::println("'{}' is a palindrome", arg);
		} else {
			std::println("'{}' is not a palindrome", arg);
		}
	}

	// EXIT_SUCCESS expands to a platform appropriate success return code
	// (usually 0).
	return EXIT_SUCCESS;
}