Programming PHP, 3rd Edition

Comparing Strings

PHP has two operators and six functions for comparing strings to each other.

Exact Comparisons

You can compare two strings for equality with the == and === operators. These operators differ in how they deal with nonstring operands. The == operator casts string operands to numbers, so it reports that 3 and "3" are equal. Due to the rules for casting strings to numbers, it would also report that 3 and "3b" are equal, as only the portion of the string up to a non-number character is used when casting it. The === operator does not cast, and returns false if the data types of the arguments differ:

$o1 = 3;
$o2 = "3";

if ($o1 == $o2) {
  echo("== returns true<br>");
}
if ($o1 === $o2) {
  echo("=== returns true<br>");
}
== returns true

The comparison operators (<, <=, >, >=) also work on strings:

$him = "Fred";
$her = "Wilma";

if ($him < $her) {
  print "{$him} comes before {$her} in the alphabet.\n";
}
Fred comes before Wilma in the alphabet

However, the comparison operators give unexpected results when comparing strings and numbers:

$string = "PHP Rocks";
$number = 5;

if ($string < $number) {
  echo("{$string} < {$number}");
}
PHP Rocks < 5

When one argument to a comparison operator is a number, the other argument is cast to a number. This means that "PHP Rocks" is cast to a number, giving 0 (since the string does not start with a number). Because 0 is less than 5, PHP prints "PHP Rocks < 5".

To explicitly compare two strings as strings, casting numbers to strings if necessary, use ...