PHP programming knowledge that is often easily forgotten
1. The difference between echo and print
The functions of echo and print in PHP are basically the same (output), but there are still subtle differences between the two. There is no return value after echo output, but print has a return value, and it returns false when its execution fails. Therefore, it can be used as a normal function. For example, after executing the following code, the value of variable $r will be 1.
$r = print "Hello World";
This means that print can be used in some complex expressions, but echo cannot. However, because the echo statement does not require any value to be returned, the echo statement in the code runs slightly faster than the print statement.
2.The difference between include and require
The functions of include() and require() are basically the same (include), but there are some differences in usage. include() is a conditional inclusion function, while require() is an unconditional inclusion function. For example, in the following code, if the variable $a is true, the file a.php will be included:
if($a){
include("a.php");
}
And require() is different from include(). No matter what value $a takes, the following code will include the file a.php into the file:
if($a){
require("a.php");
}
In terms of error handling, use the include statement. If an include error occurs, the program will skip the include statement. Although the error message will be displayed, the program will continue to execute! But require will give you a fatal error.
Of course, we can also understand Qifen literally: require means a very strong request or requirement.
3.require_once() and include_once() statements
I digress, because they look similar. Simple require_once() and include_once() statements correspond to require() and include() statements respectively. The require_once() and include_once() statements are mainly used when multiple files need to be included, which can effectively avoid errors in repeated definitions of functions or variables caused by including the same piece of code.
4. The difference between empty string ('') and NULL
Empty strings and NULL in PHP are stored with a value of 0, but their types are different. You can try echo gettype(''); and echo gettype(NULL); and you will find that they print out are string and NULL respectively. Of course, 0 is also easy to confuse. You can try echo gettype(0); if you print the type, you will find that the type of 0 is integer (integer). You can see string (''), NULL and 0 are "equal" but not of equal type.
5. The difference between isset and empty
We can understand from the literal meaning: empty is to determine whether a variable is "empty", while isset is to determine whether a variable has been set. But there is one thing you must pay attention to here: when the value of a variable is 0, empty considers the variable to be equal to empty, which is equivalent to no setting. For example, when we detect the $id variable, when $id=0, we use empty and isset to detect whether the variable $id has been configured. Both will return different values: empty thinks it is not configured, and isset can get the value of $id. , see the example below:
$id=0;
Empty($id)?print "I am empty":print "I am $id."; //Result: I am empty
!isset($id)?print "I am empty":print "I am $id.";//Result: I am 0
6. The difference between == (equal) and === (constant)
Looking back at the fourth difference between empty string ("") and NULL above, let's look at another example:
'' == NULL;
'' === NULL;
After running it, you will find that the first one is true, and the second one is false! It can be seen that == only compares whether the values are equal, while === not only compares the values, but also compares the types, which is more strict.
7. The difference between self :: and this->
When accessing member variables or methods in a PHP class, if the referenced variable or method is declared as const (defining constant) or static (declaring static), then you must use the operator::, otherwise if it is referenced The variable or method is not declared as const or static, then the operator -> must be used.
In addition, if you access a const or static variable or method from within the class, you must use self-reference. On the contrary, if you access a non-const or static variable or method from within the class, you must use self-reference. $this.
8. The difference between strstr() and strpos()
stristr() is case-insensitive strstr() is case-sensitive
Function finds the first occurrence of a string within another string.
If successful, returns the rest of the string (from the point of the match). If the string is not found, returns false.
stripos() is case-insensitive strpos() is case-sensitive
The function returns the position of the first occurrence of a string in another string.
If the string is not found, return false.
Tests have proven that if you just search to determine whether it exists, the execution efficiency of strpos() is greater than strstr()
9.HTTP_HOST and SERVER_NAME in PHP
Similarities:
When the following three conditions are met, both will output the same information.
1. The server is port 80
2. ServerName in apache’s conf is set correctly
3. HTTP/1.1 protocol specification
Differences:
1. Usually:
_SERVER["HTTP_HOST"] Under the HTTP/1.1 protocol specification, information will be output according to the client's HTTP request.
_SERVER["SERVER_NAME"] By default, the ServerName value in the apache configuration file httpd.conf is directly output.
2. When the server is not port 80:
_SERVER["HTTP_HOST"] will output the port number, for example: mimiz.cn:8080
_SERVER["SERVER_NAME"] will directly output the ServerName value
So in this case, it can be understood as: HTTP_HOST = SERVER_NAME : SERVER_PORT
3. When the ServerName in the configuration file httpd.conf is inconsistent with the domain name requested by HTTP/1.0:
httpd.conf configuration is as follows:
ServerName pprar.com
ServerAlias http://www.pprar.com
Client access domain name http://www.pprar.com
_SERVER["HTTP_HOST"] output http://www.pprar.com
_SERVER["SERVER_NAME"] output pprar.com
Therefore, in actual programs, you should try to use _SERVER["HTTP_HOST"], which is safer and more reliable.
If you are using port mapping and accessing from the intranet, it is better to use "$_SERVER['HTTP_X_FORWARDED_HOST']".
For those with basic knowledge (for example, many people have learned C in college) PHP is indeed not difficult
The purpose of PHP when it was originally developed is to quickly develop a bunch of frameworks unlike Java
But for people like you I have never been exposed to high-level programming languages
The difficult part is getting started. After all, there is a huge difference between front-end languages like HTML and CSS and high-level languages
It is recommended that if you have the conditions, you can find friends around you who can teach you the basics. Programming ideas
Basic knowledge of variables, loops, arrays, objects, functions, etc.
Then buy an introduction to PHP or download one online to see if you get used to it. Thank you for the simple code
After you feel that the basic knowledge is almost the same Download some standard source code to see how other people write the code and go to the technical forum
Then you can start writing your own website and that's it.
The more progressive development is what will happen in the future and what will be the target and the design. Models and frameworks are all used after you are familiar with the basics
and will be used for further development. Don’t worry about it at first
That won’t work for you. You need to use php tags, or process it directly in the php code. Let me give you an example:
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