Study Notes on PHP Global Variables_PHP Tutorial

Today we refer to PHP’s official introduction to PHP global variables to understand some uses of PHP global variables and some of our own thoughts on them. I hope it will be helpful to all students by sharing them now.

1. Thinking about the core points:

1. Which global variables are expired and how to deal with them?
For example: unset($GLOBALS, $_ENV, $HTTP_GET_VARS, $HTTP_POST_VARS, $HTTP_COOKIE_VARS, $HTTP_SERVER_VARS, $HTTP_ENV_VARS);
2. Which global variables are invalid on the command line?
3. How to use htmlspecialchars(), why use it?
4. What are the connections and differences between $_REQUEST and $_GET, $_POST, $_COOKIE?
5. Why is the file uploaded but the $_FILES variable does not exist or is empty?
6. What is the scope of global variables?
7. I want to get the user’s IP and browser’s user_agent information. How to get it?
8. I don’t use a browser, am I doing socket programming? How to maintain session?
9. How to obtain header information?

PHP’s nine global predefined arrays

Superglobal variables — Superglobal variables are built-in variables that are always available in all scopes
$GLOBALS — references all variables available in the global scope
$_SERVER — Server and execution environment information
$_GET — HTTP GET variable
$_POST — HTTP POST variable
$_FILES — HTTP file upload variable
$_REQUEST — HTTP Request variable
$_SESSION — Session variable
$_ENV — environment variable
$_COOKIE — HTTP Cookies
$php_errormsg — Previous error message
$HTTP_RAW_POST_DATA — Raw POST data
$http_response_header — HTTP response header
$argc — Number of arguments passed to the script
$argv — Array of arguments passed to the script

2. Main issues
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Summary topic of PHP basics:
1>. var_dump(0=="ads"); What is the result of this statement? Why?
Answer: The result of this statement is true;
The string on the right side of this expression is forced to be converted to int data 0 by default, which is the same as the data on the left side, so true is output. If it is "===", false is output. This is because they have different types and different values. , no coercion is done here.

Comment: It’s hard to say this, let’s test it! var_dump() prints the result of an expression! This actual test is about expression operations.

2>. Can exceptions be cloned?
Answer: No.

3>.What are the characteristics of Traits in PHP?
Answer: Traits (horizontal reuse/multiple inheritance) is a set of methods that are structured like a class, but it cannot be instantiated. It allows developers to easily reuse methods in different classes;
The best application of Traits is that multiple classes can share the same function;
Static variables can be referenced by trait methods, but cannot be defined by the trait. But traits can define static methods for the classes they use;
If a trait defines a property, the class cannot define a property with the same name, otherwise an error will be generated;

Summary: Good questions and good answers

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1. What are the super global variables? Answer: Super global variables: $GLOBALS, $_SERVER, $_GET, $_POST, $_FILES, $_COOKIE, $_SESSION, $_REQUEST, $_ENV

2. The browser has disabled cookies, can $_SESSION still be used? Answer: It can no longer be used
Comment: Wrong answer, it works! Apache has an automatic function to put session_id in the get parameter.

3. Is $php_errormsg available at any time? Answer: No, this variable is only available in the scope where the error occurs, and the track_errors configuration item is required to be turned on (the default is turned off).

Summary: Very positive, it would be better if the answer is more comprehensive

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Personalized interview questions
Write 30 php string functions.
Example:
trim() Remove spaces from string
chop() Deletes the specified character from right to left, parameter rtrim(string,find);
rtrim() Delete the specified character from right to left, parameter rtrim(string,find);
chr() Returns the asc2 code of the character
var_dump() Prints a value, which can be in any form, and returns the value's attributes
print() Print array or string
print_r() simply prints strings and numbers, while arrays are displayed as a bracketed list of keys and values ​​
chunk_split() Split the string into a series of smaller parts
implode() Combines array elements into a string
join() Combines array elements into a string
explode() Split the string into arrays
md5() Returns an md5 value, irreversible
strlen() Get the length of a string
str_replace Replace some characters in the string
mb_substr mb extended interception string function, format: mb_substr(string,start_Num,end_Num,'utf-8')
str_split Split a string into an array according to the character spacing
strpos Find and return the position of the first match
strtr Convert specific characters in the string
substr Intercept the string
substr_count Counts the number of occurrences of a certain character segment in a string
substr_replace Replace some characters in the string
The wordwrap function wraps a string according to the specified length
addcslashes() Adds a backslash
before the specified character strtolower() Convert the string to lowercase
strtoupper() Convert string to uppercase
strrev() Reverse string
strripos() Find the last occurrence of a string in another string (case insensitive)
strrpos() Find the last occurrence of a string in another string (case sensitive)
strspn() Returns the number of specific characters contained in the string
ucwords() Converts the first character of each word in the string to uppercase
str_repeat() Repeat the string the specified number of times
...

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1. Does the namespace have to be the first statement of the program script?
Answer: yes

2. How to cancel the reference?
Answer: unset();

3. If at least one method in a class is declared abstract, does this class have to be declared abstract? When inheriting an abstract class, does the subclass have to define all abstract methods in the parent class?
Answer: If there are abstract methods in a class, the class must be defined as an abstract class. When inheriting an abstract class, the subclass must define all abstract methods in the parent class.

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1. How to get the absolute path of the file
Use the realpath() function to return the absolute path name. If it fails, it returns false, for example the file does not exist.
echo realpath("test.txt");
Output:
C:wwwtestwebtest.txt

2. How session works
The session is saved on the server, but a sessionid is saved on the client in the form of a cookie. If cookies are disabled, you need to use the URL rewriting mechanism of the get method or use the POST method to submit a hidden form.

Comments: This is the principle, but generally a web server will automatically complete this function, and there is no need to add it in the program.

3. Is the function declared by public static a static method?
The function declared by public static is a static method and can be used directly outside the class. The method call of class name::function name does not need to be declared in the NEW way
Note: There cannot be dynamic content within the function such as $this->
Generally speaking, content that needs to be executed frequently is declared with STATIC

Summary: The working principle of session is well organized and analyzed thoroughly. I hope to be more positive in the future and continue to work hard

http://www.bkjia.com/PHPjc/632673.htmlwww.bkjia.comtruehttp: //www.bkjia.com/PHPjc/632673.htmlTechArticleToday we refer to PHP’s official introduction to PHP global variables to understand some usage of PHP global variables and some of our own opinions on them Think about it and share it now. I hope it will be helpful to all students. One...