Find preprocessor guards in a C/C++ file

finddef.php

<?php

namespace finddef;

set_error_handler(function($errno, $errstr, $errfile, $errline, $errcontext) { echo "Execution error: {$errstr} on line {$errline} of {$errfile}" . PHP_EOL; exit; });

function make_check_ident($ident) {
	$ident = preg_quote($ident, '~');
	return function($no, $text) use($ident) { return 1 === preg_match("~\b{$ident}\b~", $text); };
}

function make_check_lineno($lineno) {
	return function($no, $text) use($lineno) { return $no === $lineno; };
}

function is_guard_start($text) {
	return 1 === preg_match("~^#\s*if(n?def)?\b~", $text);
}

function is_guard_alt($text) {
	return 1 === preg_match("~^#\s*el(se|if)\b~", $text);
}

function is_guard_end($text) {
	return 1 === preg_match("~^#\s*endif(n?def)?\b~", $text);
}

function print_line($no, $text) {
	echo "{$no}:\t{$text}" . PHP_EOL;
}

function print_guards($guards) {
	foreach ($guards as $guard) {
		list($no, $text) = $guard;
		print_line($no, $text);
	}
}

function find($file, $check) {
	$guards = [];
	$lineno = 0;
	while (!feof($file)) {
		$lineno++;
		$linetext = rtrim(fgets($file));
		if ($check($lineno, $linetext)) {
			print_guards($guards);
			print_line($lineno, $linetext);
			echo PHP_EOL;
		}
		if (is_guard_end($linetext)) {
			array_pop($guards);
		}
		if (is_guard_alt($linetext)) {
			$guard = array_pop($guards);
			array_push($guards, [ $lineno, "{$linetext} [ {$guard[0]}: {$guard[1]} ]" ]);
		}
		if (is_guard_start($linetext)) {
			array_push($guards, [ $lineno, $linetext ]);
		}
	}
}

if ($argc !== 3) {
	echo "Usage: {$argv[0]} FILE (IDENT | LINENO)" . PHP_EOL;
	echo "Finds in FILE what preprocessor directives guard the occurences of IDENT or line number LINENO." . PHP_EOL;
	exit;
}

$file = fopen($argv[1], 'rt');
if (!$file) {
	exit;
}

$check = ctype_digit($argv[2]) ? make_check_lineno((int)$argv[2]) : make_check_ident($argv[2]);

find($file, $check);