nl2br();// n to
addslashes(); stripslashes();//Escape special characters when operating on the database
chop();//Remove spaces on the right side of the string
trim();// Remove all spaces in the string
ltrim();//Remove the spaces on the left side of the string
htmlspecialchars();//Convert '$','"','<','>' to the corresponding html entities
htmlentities();//Convert all html tags into corresponding html entities
array explode(string separator, string str);//Split the string
string implode(string separator, array arr);//Connect the string
strtoupper(); strtolower();//Convert uppercase to uppercase
ucfirst();//Convert only the first character to uppercase
ucwords();//Convert the first letter of each word to uppercase