Special operation symbols and functions commonly used in PHP development

Annotation symbols:

// Single-line annotation

/* */Multi-line annotation

' ' Single quotation mark, a simple string, taken directly without any processing;
" "Double quotation mark, PHP dynamically processes and then outputs it, generally used to process $variables.
Boolean variables:
One is true, which is true;
The other is false, which is false.
Common variables:
string String ( Numbers\Chinese characters\etc.)
integer integer (1, 2, 3, 4, 5, 0, -1, -2, etc.)
double floating point number (decimal point)
array array
object Object
The methods that can be used are gettype($mix) and settype($mix,$typename);

Commonly used symbol escapes:
\" Double quotes
\\ Backslash
\n Newline
\r Return to the beginning of the line
\t Horizontal tab
Operation symbols:
+ Addition operation - Subtraction operation
* Multiplication operation/Division operation
% Take the remainder ++ Add 1 to yourself
-- Subtract 1 to yourself. Connect two strings
Assignment operation:
= Substitute the value on the right into the left
+= Add the value on the right to the left
-= Subtract the value on the right to the left
*= Multiply the value on the left by the right
/= Add the value on the left Divide the value by the right side
.= Add the string on the right side to the left side
Bitwise operations:
& Bitwise AND
| Bitwise or
^ Bitwise Exclusive OR (xor)
<< Shift 1 bit to the left
>> Shift 1 bit to the right
~ Complement
Logical operation:
< Less than> Greater than
<= Less than or equal to>= Greater than or equal to
!= Not equal to && and
|| or! Other operation symbols other than

$ Variable symbol
& Variable alias
@ Do not display error message (add before function)
-> Method or property of object
=> Element value of 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

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

3. About quotation marks

1. Single quotation marks are output as they are
2. Double quotation marks are content interpretation and output
3. Anti-single quotation marks (small quotation marks) 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" which is a newline.

4.函数:htmlspecialchars() 和 htmlentities()
本函数将特殊字符转成 HTML 的字符串格式 ( &....; )。最常用到的场合可能就是处理客户留言的留言版了。

& (和) 转成 &
" (双引号) 转成 "
< (小于) 转成 <
> (大于) 转成 >
(空格)转成

5.批量输出HTML内容！

echo <<< EOT
HTML输出内容。。。//这里注释照样输出！
EOT;

print <<HTML输出内容。。。//这里注释照样输出！
EOT;
(注意：内部包含变量用“{变量}”)

6.判断文件是否存在并且输出内容file_exists ()

7.删除变量释放内存unset();

unset($var);
unset($var,$var1);

8.is_numeric;
检测变量是否是数字;

9.is_int;
检测变量是否是整数;

10.is_null;
检测变量是否为 NULL ;

11.is_string
检测变量是否是字符串

12.is_real;
is_float() 的别名

13.isset
检测变量是否定义

14.is_bool
检测变量是否是布尔型

15.is_array
检测变量是否是数组

16.is_object
检测变量是否是一个对象

17. The substr() function returns a part of the string.

substr (String,Start,SelectNum)

.code show as below:

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() turns the escaped newline into html

.code show as below:

echo nl2br("foo isn't\n bar");

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