How to use string functions in PHP

There are many ways to use the string functions in PHP, including the following:

(1) echo, print, printf, sprintf
The first two functions are output strings. if there is a variable name in the string, it is replaced with its value.
The last two functions are similar to C functions with the same name.

(2) strchr, strlen, strtok, strrchr, strrev, strstr, strtolower,
Strtoupper, substr, ucfirst
These are commonly used string operation functions, and some of them are exactly the same as the functions of the same name in C.
Strrev is used to flip a string.
The meaning of strtolower and strtoupper should not be explained.
Ucfirst converts the first character of a string to uppercase.
Substr is a substring of the returned string. its usage is substr (string, header, length ).
The header position is counted from 0. if it is a negative number, it indicates the forward number from the tail.

(3) Chr, Ord
Similar to C functions with the same name.

(4) explode, implode, join
These are functions related to arrays.
Explode (string, delimiter) returns an array generated when the string is split.
Implode (array, delimiter) returns a string that inserts a delimiter into each element of the array.
Join and implode have the same meaning.

(5) Chop
Removes the white space at the end of the string.

(6) htmlspecialchars
Replace the special HTML characters in the string with their names, for example, \ "<\" into \ "<\".

(7) nl2br
Add \ "before each carriage return in the string \"
\".

(8) AddSlashes, StripSlashes
Add \ "\" to the string to be used for database query, and remove \"\\".

(9) parse_str
Analyze a string of the \ "name1 = value1 & name2 = value2 &... \" type into some variables.
For example:
Parse_str (\ "a = 1 & B = 2 \");
Generate two variables, $ a and $ B. The values are 1, 2, respectively.
If two pairs of names/values have the same name, the latter value overwrites the previous one.
If both pairs have \ "[] \" at the end, for example \ "a [] = 1 & a [] = 2 \", an array $ a is generated, the two elements are respectively 1, 2