Common functions for PHP to process strings

（1）trim() Remove whitespace and other characters on both sides of the string ;

（2）strlen() Gets the length of the string

（3）mb_strlen() Get string length （ Character encoding can be specified , Calculate the length of Chinese string ）

（4）substr() Returns part of a string ;

（5）str_replace() Substring replacement

（6）str_repeat () Duplicate a string

（7）is_string() Check if the variable is a string ;

（8）str_shuffle () Randomly scramble a string

（9）sprintf() Returns the string generated from the formatted string （ Usually used to get the data table name after the sub table ）

（10）strstr() First occurrence of lookup string

（11）addslashes Use backslashes to reference strings