The difference between echo() and print(), require() and include() and other easily confused functions in PHP_PHP Tutorial

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 still Will continue to implement! 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’m off topic, because they look like, simple require_once() and include_once() statements respectively correspond to require () and include() statements. The require_once() and include_once() statements are mainly used when multiple files need to be included, which can effectively avoid the error of repeated definition 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 both stored with a value of 0, but their types It's not the same. 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); If you print the type, 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 of different types.

5. The difference between isset and empty

From the literal meaning, we can understand: empty is to judge whether a variable is "empty", while isset is to judge whether 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:
$id=0;
emptyempty($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 0

6.== (etc.) and == = (Identity) difference

Review the difference between the fourth 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.

http://www.bkjia.com/PHPjc/325144.htmlwww.bkjia.comtruehttp: //www.bkjia.com/PHPjc/325144.htmlTechArticle1. The difference between echo and print The functions of echo and print in PHP are basically the same (output), but the difference between the two There are still subtle differences. There is no return value after echo output, but print has a return value. When...