Isset and empty look like functions. We often use them as functions, but they are actually language constructors. The language constructor in php is equivalent to the predefined macro in C. It is a keyword defined in the php language and cannot be modified or disabled. The function in php is different. It is a function and is executed
Isset and empty look like functions. We often use them as functions, but they are actually language constructors. The language constructor in php is equivalent to the predefined macro in C. It is a keyword defined in the php language and cannot be modified or disabled. The function in php is different. It is a function and is executed
Isset and empty look like functions. We often use them as functions, but they are actually language constructors.
The language constructor in php is equivalent to the predefined macro in C. It is a keyword defined in the php language and cannot be modified or disabled.
The functions in php are different. They are functions that will be parsed during execution and then passed in parameter calculation.
Therefore, the execution efficiency of functions is not as high as that of the language constructor.
For example, we can determine whether an array contains a key. Using isset ($ arr [$ key]) is more efficient than array_key_exists ($ arr, $ key.
The language constructor in php includes:
Echo
Print
Die
Isset
Unset
Include
Require
Array
List
Empty
References
Http://blog.sina.com.cn/s/blog_475429950100hk75.html