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PHP Learning String Comparison and Search_PHP Tutorial

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Release： 2016-07-21 15:30:47

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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, while the triple equal sign will compare types, but 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 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 (1st~ 3 results are incorrect, only the 4th one is correct):

Copy 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 String insertion and deletion operations can be implemented. 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 character that repeats count times string string.
５. Filling string
$newstring = str_pad(to_pad, length[, with[, type]]);
There are three types of types: STR_PAD_RIGHT (default), STR_PAD_LEFT and STR_PAD_BOTH; with default is Space. The function indicates that the to_pad string is filled with with into a string with a length of 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) ; ('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 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 for reading strings.
When strtok is marked, use strtok($str, $token) to initialize, and use strtok($token) to continue to obtain the value. The code is as follows:

Copy 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 of 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 not to distinguish between sizes Search; strchr is an alias of 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', 65); // "a hello world program" 
$str = strrchr('This a hello world program', 65); ', ' '); // " 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 Processing