photoshop learning network PHP learning string comparison and search

1. String comparison
In PHP, you can use == (double equal sign) or === (triple equal sign) to compare strings. The difference between the two is that the double equal sign does not compare types, and the triple equal sign will compare types, but it does not convert types; when comparing with a double equal sign, if there is a numeric value on the left and right sides of the equal sign, the other value will be converted as a number and then compare. In this case, if it is a pure string or NULL, it will be converted to 0 for comparison. Similarly, the greater than or equal sign is the same as the equal sign, and incorrect results may occur during comparison.
So, you can use PHP’s built-in functions strcmp and strcasecmp to compare strings. Among them, strcasecmp is a variant of strcmp. It converts the string to lowercase first and then compares it. The following code:

Copy the code The code is as follows:

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):

Copy the code The code is as follows:

bool (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);
Return a new string that repeats count times string.
５. Filling string
$newstring = str_pad(to_pad, length[, with[, type]]);
The types include: STR_PAD_RIGHT (default), STR_PAD_LEFT and STR_PAD_BOTH; with defaults to spaces. The function indicates that the to_pad string is filled with with into a string of length length. The following code:

Copy code The code is as follows:

// 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 reverse 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
// Filling characters 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. Decomposing strings
In PHP, use explode to decompose strings, implode to merge (join is an alias of implode), and strtok to mark. 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 for reading strings.
When marking strtok, use strtok($str, $token) to initialize, and use strtok($token) to continue to obtain the value.
The code is as follows:

Copy the code The code is as follows:

$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; stristr 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.
Sample code:

Copy code The code is as follows:

$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
$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

Reference: PHP Programming, 2003, Chapter 4 Strings, String Comparison; String Search and Sum deal with

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