请教一个函数

请问一个函数
我PHP是菜鸟，判断一变量$a中是否包含另外一个变量中$b的字符，用什么方法可以实现，谢谢


------解决方案--------------------
strpos

$mystring = 'abc ';
$findme = 'a ';
$pos = strpos($mystring, $findme);

// Note our use of ===. Simply == would not work as expected
// because the position of 'a ' was the 0th (first) character.
if ($pos === false) {
echo "The string '$findme ' was not found in the string '$mystring ' ";
} else {
echo "The string '$findme ' was found in the string '$mystring ' ";
echo " and exists at position $pos ";
}

// We can search for the character, ignoring anything before the offset
$newstring = 'abcdef abcdef ';
$pos = strpos($newstring, 'a ', 1); // $pos = 7, not 0
?>