对strpos()函数可以用来在php中查找子字符串。strpos()函数将试图找到子字符串在源字符串中首次出现的位置。如果找到了，它会返回一个非负整数表示子字符串出现的位置。 否则它会返回一个布尔值false。

<?php
$haystack1 = "2349534134345w3mentor16504381640386488129";
$haystack2 = "w3mentor234953413434516504381640386488129";
$haystack3 = "center234953413434516504381640386488129fyi";
$pos1 = strpos($haystack1, "w3mentor");
$pos2 = strpos($haystack2, "w3mentor");
$pos3 = strpos($haystack3, "w3mentor");
print("pos1 = ($pos1); type is " . gettype($pos1) . "\n");
print("pos2 = ($pos2); type is " . gettype($pos2) . "\n");
print("pos3 = ($pos3); type is " . gettype($pos3) . "\n");
?>

pos1 = (13); type is integer
pos2 = (0); type is integer
pos3 = (); type is boolean
  
pos3返回的是bool值，即没有找到子字符串