Summary of commonly used special operation symbols and functions in PHP (a must-read for newbies to PHP)

Summary of commonly used special operation symbols and functions in PHP (a must-read for newbies to PHP)_PHP Tutorial

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Release： 2016-07-21 15:13:29

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注解符号:
         // 单行注解
             多行注解
引号的使用
         '   ' 单引号,简单字符串,不经任何处理直接拿过来;
         " "双引号,php动态处理然后输出,一般用于处理$变量.
布尔变量:
          一种是true 即真的;
         另一种是false 即假的
常见变量:
         string          字串(数字\汉字\等等)
         integer         整数(1、2、3、4、5、0、-1、-2、等等)
         double          浮点数（小数点）
         array           数组
         object          对象
可以用的方法有gettype($mix) 和settype($mix,$typename);

常用符号转义：

" " Double quotes
" \ Backslash
n n Line feed
r Return to the beginning of the line
t Horizontal tabulation
Arithmetic symbols:
+ Addition operation -Rugging operations *multiplication operation /division of the method
%remains ++ self -plus 1
-self -reduction 1. Connect two string

assignment operation:

/= Divide the value on the left by the value on the right
.= Add the string on the right to the left

Bitwise operations:

^ Bitwise exclusive OR (xor) <
!= is not equal to && and || or ! Other operation symbols other than

$ Variable symbol
Alias for variable
@ Do not display error message (added before function)
-> Object method or attribute
=> The element value of the array
?: Ternary operator

Commonly used basic methods:

1. PHP converts strings to upper and lower case!

strtolower(); Convert characters to lowercase
strtoupper(); Convert characters to uppercase

2.PHP encrypted string

Irreducible:
md5();
sha1();
Reducible:
base64_encode();
base64_decode();

3. About quotation marks

1. Single quotes are output as is
2. Double quotes are content interpretation and output
3. Anti-single quotes (small quotes) are used to execute a system command, such as `dir`. Commonly used in table names and field names.
4. "" acts on translation characters, such as "n" for newline.

4. Functions: htmlspecialchars() and htmlentities()
This function converts special characters into HTML string format ( &....; ). The most commonly used occasion may be the message board for processing customer messages.

& (and) is converted to &
" (double quotes) is converted to "
< (less than) is converted to <
> (greater than) is converted to >
(space ) into

5. Batch output HTML content!

echo <<< EOT
HTML output content. . . //Comments here are still output!
EOT;

print <<HTML output content. . . //Comments here are still output!
EOT;
(Note: Use "{variable}" for internally included variables)

6. Determine whether the file exists and output the content file_exists ()

$FileName="File.TXT";
if (file_exists($FileName)){
echo "

".file_get_contents($FileName)."< ;/pre>";
}else
{
echo "no";
}
?>
7. Delete variables to release memory unset();
unset($var);
unset($var,$var1);
8.is_numeric;
Detect whether the variable is a number; 
9.is_int;
Detect whether the variable is an integer;
10.is_null;
Detect whether the variable is NULL;
11.is_string
Detect whether the variable is a string
12.is_real;
alias of is_float()
13.isset
Check whether the variable is defined
14.is_bool
Detect whether the variable is of Boolean type
15.is_array
Detect whether the variable is an array
16.is_object
Detect whether the variable is an object
17.substr() function returns a part of the string. 
substr (String,Start,SelectNum)


Copy code The code is as follows:


echo substr('abcdef', 1); // bcdef
echo substr('abcdef', 1, 3); // bcd
echo substr('abcdef', 0, 4); // abcd
echo substr('abcdef ', 0, 8); // abcdef
echo substr('abcdef', -1, 1); // f


18.nb2br() Convert the escaped newline into html



Copy code The code is as follows:


echo nl2br("foo isn'tn bar");





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