Detailed explanation of PHP string comparison and search methods

var_dump(0 == 'test');
var_dump(0 == '');
var_dump(5 > 't');
var_dump(strcmp(5, 't'));

The result is (the 1st to 3rd results are incorrect, only the 4th one is correct): 4bool(true) bool(true) bool(true) int(-1) 2. String processing 1. Substring $sub = substr(string, start[, length]); 2. Substring replacement $newstring = substr_replace(string, new, start[, length]); Use this function to implement string insertion and deletion operations. The start and length of this function can be negative numbers. Respectively means counting from the end and retaining the last few digits without replacement. 3. String reverse order $newstring = strrev(string); 4. Repeat string $newstring = str_repeat(string, count); Returns a new string that repeats count times. 5. Fill in the string $newstring = str_pad(to_pad, length[, with[, type]]); Among them, there are three types: str_pad_right (default), str_pad_left and str_pad_both; with defaults to spaces. The function means to fill the to_pad string with with into a string of length length. The following code:

// Substring
var_dump(substr('1234567890', 8)); // 90
var_dump(substr('1234567890', 0, 2)) ; // 12
// Reverse substring
var_dump(substr('1234567890', -8)); // 34567890
var_dump(substr('1234567890', -8, -2)); // 345678
var_dump (substr('1234567890', -8, 2)); // 34
// Insert
var_dump(substr_replace('1234567890', 'a', 0, 0)); // a1234567890
// Delete
var_dump(substr_replace('1234567890', '', 8)); // 12345678
// Delete in the opposite direction
var_dump(substr_replace('1234567890', '', -2, -1)); // 123456780
// Replace
var_dump(substr_replace('1234567890', 'a', 0, 1)); // a234567890
// Replace in the opposite direction
var_dump(substr_replace('1234567890', 'a', -2 , -1)); // 12345678a0
// String reverse
var_dump(strrev('1234567890')); // 0987654321
// Repeat String
var_dump(str_repeat('12', 3)); // 121212
// Fill string
var_dump(str_pad('a', 10, '12')); / / a121212121
var_dump(str_pad('a', 10, '12', str_pad_left)); // 121212121a
var_dump(str_pad('a', 10, '12', str_pad_both)); // 1212a12121

3. Decompose string In PHP, explode is used to decompose a string, implode is used to merge (join is an alias of implode), and strtok is used to mark a string. There is another function slipt that can also be decomposed (regular decomposition), but it is no longer recommended in versions after 5.3. In addition, there is a sscanf() function in php, which is used to read strings. When marking strtok, use strtok($str, $token) to initialize, and use strtok($token) to continue to obtain the value. Code:

$str = '1,2,3';
$arr1 = explode(',', $str); // array('1', '2', '3 ')
$arr2 = explode(',', $str, 2); // array('1', '2,3')
$str1 = implode(',' , $arr1); // '1,2,3'
$str2 = strtok($str, ','); // 1
$str3 = strtok(',') ; // 2
$str4 = strtok(','); // 3
// array(86, 10, 88888888, 'beijin')
$arr3 = sscanf('+86 (10)88888888 beijin', '+%d(%d)%d %s');

4.String search In php, there are three series for string search. Returns the position, returns the string, and matches the number of masks. Among them, there are two functions that return positions, strpos() and strrpos(); there are also two functions that return strings, strstr() and strchr(); functions that return mask matching numbers include strspn() and strcspn() . strpos means counting from the left and returns the position where the string to be found first appears; strrpos means counting from the right and returns the position where the string to be found first appears. strstr means counting from the left and returns the substring from the first to the end of the string to be searched (including the search string). When searching for characters, you can use ASCII code numbers to represent characters; strstr means size-insensitive search; strchr Is an alias for strstr; strrchr returns the substring from the last occurrence of the character to the end. strspn means counting from the left, the number of characters of the substring before the first non-masked occurrence; strcspn means counting from the left, the number of characters of the substring before the first occurrence of the mask. Code:

$pos = strpos('this a hello world program', ' '); // 4
$pos = strpos('this a hello world program', 32); // 4
$pos = strrpos('this a hello world program', ' '); // 18
$pos = strrpos('this a hello world program', 32); // 18< ;/p>
$str = strstr('this a hello world program', ' '); // " a hello world program"
$str = strstr('this a hello world program', 32) ; // " a hello world program"
$str = stristr('this a hello world program', ' a'); // "a hello world program"
$str = stristr ('this a hello world program', 65); // "a hello world program"
$str = strrchr('this a hello world program', ' '); // " program"
$str = strrchr('this a hello world program', 32); // " program"
$str1 = "12345 12345 12345";
$len = strspn($ str1, '12345'); // 5
$len = strcspn($str1, ' '); // 5