PHP string function (2): comparison operation

* 1.strcmp($str1, $str2): Binary safe string comparison

* 2.strncmp($str1, $str2, $length): Compare whether the length specified at the beginning is the same

* 3.strcasecmp($str1, $str2): Binary safe string comparison, case-insensitive

* 4.strncasecmp($str1, $str2): Binary safe string comparison , case-insensitive

* 5.strspn($str,$mark,$start,$length): Get the length of the starting substring matching the mask

* 6. strcspn($str,$mark,$start,$length): Get the length of the starting substring of the unmatched mask

$str1 = 'php中文网';
$str2 = 'PHP中文网';

//1.strcmp($str1, $str2):String For comparison, return 0 if equal, return >0 if greater, otherwise return <0

echo strcmp($str1, $str2) == 0 ? &#39;相等&#39; : &#39;不相等&#39;, &#39;<br>&#39;;

//2.strncmp($str, $str2, $n): Compare whether the lengths specified at the beginning are equal

echo strncmp($str1, $str2, 3) == 0 ? &#39;相等&#39; : &#39;不相等&#39;, &#39;<br>&#39;;

//3.strcasecmp($str1, $str2): case-insensitive string comparison, returns 0 if equal, >0 if greater, otherwise returns <0

echo strcasecmp($str1, $str2) == 0 ? &#39;相等&#39; : &#39;不相等&#39;, &#39;<br>&#39;;

//4 .strncasecmp($str1, $str2): Case-insensitive comparison of whether the length specified at the beginning is equal

echo strncasecmp($str1, $str2,3) == 0 ? &#39;相等&#39; : &#39;不相等&#39;, &#39;<br>&#39;;

//5.strspn($str, $mark, $start, $length):

//Calculate the length of the first substring in which all characters in the string exist in the specified character set

//$str1: The string to be compared, $mark: Similar to a set, return Number of matches

echo strspn(&#39;15705519989&#39;, &#39;1234567890&#39;),&#39;<br>&#39;;  //返回11

//You can specify the position and length to start comparison

echo strspn(&#39;15705519989&#39;, &#39;1234567890&#39;, 4, 4),&#39;<br>&#39;;//返回4

//Only compare the first substring in $str, ignore all the following ones, and return 11

echo strspn(&#39;15705519989 18955123344 111abc&#39;, &#39;1234567890&#39;),&#39;<br>&#39;;

//Return 3, because only the first three in the first string are data belonging to the number set

echo strspn(&#39;157php 18955123344 111abc&#39;, &#39;1234567890&#39;),&#39;<br>&#39;;

//For example, the mobile phone number must be a pure numeric string, requiring the user What must be entered is a purely numeric string

$phone = '13899886767';

// $phone = '1389988php6767';

$mark = '0123456789';

//Analysis, if it matches correctly, strspn() must return 11, because the phone The number is 11, which is exactly the same as strlen($phone)

echo strlen($phone)==strspn($phone, $mark) ? '全数字' : '必须全为数字';

//Equivalent to: strspn(substr($subject, $start, $length), $mask)

// 6. The functions of strcspn() and strspn() are exactly opposite. You can verify it by giving examples