PHP: Avoid the equal ("==") comparison operator for comparing strings that may be numeric.

string_comparison_example.php

<?php
/*
 * When using the equal comparison operator ("==") to compare a number with a string or
 * the comparison involves numeric strings, each string is converted to a number and the
 * comparison performed numerically. These rules also apply to the switch statement. The
 * type conversion does not take place when using the identical comparison operator
 * ("===") as that involves comparing the type as well as the value.
 *
 * It's safer to always use strcmp() or the identical comparison operator ("===") for
 * string comparisons.
 *
 * Based on PHP documentation at: http://php.net/manual/en/language.operators.comparison.php
 */

test("1234", "1234");
test("1234", " 1234");
test("1234", "\n1234");
test("1234", "1234 ");
test("1234", "1234\n");

function test($x, $y) {
	echo var_dump_str($x) . ' vs. ';
	echo var_dump_str(show_cr($y)) . PHP_EOL;

	$strcmpTest = (strcmp($x, $y) == 0);
	$equalTest = ($x == $y);
	$identicalTest = ($x === $y);

	echo 'strcmp() test: ' . var_export($strcmpTest, true) . PHP_EOL;
	echo 'equal test: ' . var_export($equalTest, true) . ' ' .
		(($equalTest == $strcmpTest) ? 'AGREE' : 'DISAGREE') . PHP_EOL;
	echo 'identical test: ' . var_export($identicalTest, true) . ' ' .
		(($identicalTest == $strcmpTest) ? 'AGREE' : 'DISAGREE') . PHP_EOL;
	echo PHP_EOL;
}

function show_cr($var) {
	return str_replace("\n", "\\n", $var);
}

function var_dump_str($var) {
	ob_start();
	var_dump($var);
	$dump = trim(ob_get_contents());
	ob_end_clean();
	return $dump;
}

/*
 * Results:
 *
 * string(4) "1234" vs. string(4) "1234"
 * strcmp() test: true
 * equal test: true AGREE
 * identical test: true AGREE
 *
 * string(4) "1234" vs. string(5) " 1234"
 * strcmp() test: false
 * equal test: true DISAGREE
 * identical test: false AGREE
 *
 * string(4) "1234" vs. string(6) "\n1234"
 * strcmp() test: false
 * equal test: true DISAGREE
 * identical test: false AGREE
 *
 * string(4) "1234" vs. string(5) "1234 "
 * strcmp() test: false
 * equal test: false AGREE
 * identical test: false AGREE
 *
 * string(4) "1234" vs. string(6) "1234\n"
 * strcmp() test: false
 * equal test: false AGREE
 * identical test: false AGREE
 */