PHP Learning Note--6. String

1. How to define

① Double Quote method

Example: $str = "Hello";

Note: When you use double quotation marks for string definitions, you cannot have double quotes inside the string

Because PHP will parse it as a string boundary

Example: $str = "Hello," "Susan"; =>hello,

In this case, internal double quotes can be escaped, using \ "for non-semantic"

Then: $str = "hello,\" susan\ "";

Other symbols that need to be escaped:

\ "= =" \ n "+" \ \ =

\ r = Return \$ = $ \ ' = '

② Single-Quote method

PHP does not make complex escapes by using single-quote-defined strings

Only escape \ ' and \ \ All other outputs as-is

Single-quote string of $: Output directly as a string

and double quotes will try to parse it as a variable.

How do I select single/double quotes?

Large pieces of text, using single quotes, parsing fast

If you do want to enclose the variable in a string, you need to use double quotation marks

③heredoc notation

<<< identifiers

Large paragraph of text (containing double quotes, single quotes)

Identifier = = must have an exclusive line and no characters in front of it

Function: Consistent with double quotes, resolves internal escapes, variables, etc.

④nowdoc notation

<<< ' identifiers '

Large paragraph text

Identifier

Function: Consistent with single quotation marks

2. Class array attributes for strings

Example: $str = ' abcdef ';

echo $str [0]; =>a

3. String length function

strlen (string variable); = = Calculates the number of string bytes

Note: A Chinese character occupies three bytes in UTF-8

Mb_strlen (string variable, [character set]); = = Calculates the number of string characters

4. Finding the string neutron character position function

Strpos (string variable, ' find target ', [offset]); + = Calculates how many characters are the target characters from the beginning

Note: The object that the function looks for is case-sensitive

If the ' Find target ' fills in an integer, the integer is converted to an ASCII code

In the ASCII code:

65~90 = a~z 97~122 = a~z

If the first (0) is the target at the time of the If judgment, false is returned, and the = = = is used to judge

Example: if (Strpos () ===false) {

return false;

}else{

return true;

}

Offset is skipped by a certain number and then looked up

Stripos () = function Ibid., the target of which it is found is not case-sensitive

Strrpos () = The location of the last occurrence of the target character

Substr_count () = count the number of occurrences of the target

5. String substitution function

Str_replace (' Primitive ', ' replace ', string variable, [number of substitutions]);

' Primitive ' and ' replace ' are mixed types, such as arrays

If you replace two at a time, always start from scratch.

STRTR (string variable, ' primitive ', ' replace ');

' Primitive ' corresponds to ' replace with ', one character is substituted for one character

Example: ' Hi ' and ' ab ' are h=>a i=>b

In practical applications, full/half-width conversion is possible.

6. String intercept function

SUBSTR (string variable, starting from where, [to which end]);

From where to start if you fill in a negative number, proceed from right to left

Example: substr (' 123456 ', 2,-2); =>34

STRSTR (string variable, target character, [true]);

Intercept the first occurrence of the target character ~ end of the section

If you increase the true option, it is the ~ start part

STRRCHR (string variable, target character, [true]);

Intercept the last occurrence of the target character ~ end of the section

Can be used to determine file formats in real-world applications

7. Splitting, linking, and reversing functions of strings

Ltrim (string variable, ' need to trim character ');

Rtrim (string variable, ' need to trim character ');

Str_split (string variable, [n]);

Divides a string into a group of n letters, forming an array in the aggregate

Explode (' separator ', string variable);

Divides a string into groups with the specified delimiter, forming an array as a whole

Implode ([' Connector '], array variable);

Concatenate all cell values in an array into a single string with a connector

Chunk_split (string variable, several characters apart, [' Add character ']);

Example: Chunk_split ($STR, 3, ', '); = = Adds a comma to the $STR string every 3 characters

Increase the line break automatically if you do not fill in the added characters

Strrev (string variable); = = Invert string ABC=>CBA

8. String Escape function

Addslashes (string variable);

Special characters, such as single quotes, can be destructive when working in a database.

When the user enters a single quotation mark, the function can be escaped by adding \ in front of the single quotation mark

Stripslashes (string variable);

Convert special characters to HTML entities, such as < > = $LT; $GT;

Htmlspecialchars_decode (string variable);

Convert an HTML entity to a special character

9. String comparison function

strcmp (' String 1 ', ' String 2 '); = = Returns the bool value

10. String Conversion Functions

Strtolower (string variable); = = ALL Caps

Strtoupper (string variable); = = All lowercase

Ucfirst (string variable); = = First Letter capitalized

11. System functions

PathInfo (string variable); = = Returns its information, such as name, suffix, etc.

Number_format (string variable); = = The string is represented in thousands of bits 1,234,567

@zhnoah
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PHP Learning Note--6. String