Programming PHP

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 non-string operands. The == operator casts non-string operands to strings, so it reports that 3 and "3" are equal. The === operator does not cast, and returns false if the 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 the strcmp( ) function:

$relationship = strcmp(string_1, string_2);

The function returns a number less than 0 if string_1 sorts before string_2, greater than 0 if string_2 sorts ...