What is the difference between php echo(), print(), require() and include() functions

A brief summary of the differences between echo() and print(), require() and include() and other easily confused functions

1. The difference between echo and print

## The functions of echo and print in #PHP are basically the same (output), but there are 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 $a is. value, 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 inclusion error occurs, the program will skip the include statement, Although 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

are off topic, 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

Both empty strings and NULL in PHP are stored with a value of 0, but their types are not the same. It’s different. You can try echo gettype(”); and echo gettype(NULL); and you will find that they print string and NULL respectively. Of course, 0 is also easy to confuse. You can try echo gettype(0) ;Print the type and you will find that the type of 0 is integer (integer). It can be seen that string ("), NULL and 0 are "equal values" but not equal types.

5.isset and The difference between 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. Get up: When the value of a variable is 0, empty considers the variable to be equal to empty, which is equivalent to not being set. For example, when we detect the $id variable, when $id=0, use empty and isset to check whether the variable $id has been set. Configuration, both will return different values: empty thinks there is no configuration, isset can get the value of $id, see the example below:

$id=0;
emptyempty($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 empty : I am 0

6. The difference between == (equal) and === (equal)

Review the fourth empty string ("" ) and NULL, let’s look at another example:

” == NULL;

” === NULL;

After running, you will find that the first one is true, and the The two are 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.

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