Why don't variables in php need to be specifically declared?

As the title states, there is no need to declare variables in PHP. Does the system know what a variable is and allocate space to the variable based on $? Does it not need to declare variables because php is a weakly typed language?

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The question is like the title, there is no need to declare variables in PHP, so does the system know what variables are and allocate space to variables based on $? Does it not require declaring variables because php is a weakly typed language?

The underlying C of PHP uses a union to store variables. There are various variable types in this union. PHP uses long type to store integers and hashtable to store arrays, because union can store various variables. , and the interpreter will automatically determine the variable type, so PHP does not need to declare the variable type, weak type

Yes, because php is a weakly typed language, there is no need to declare the variable type before it can be used. .

$ is just syntax sugar, indicating that what follows is a variable. .

If explained in terms of memory space allocation

• When allocating memory space for weakly typed variables, this memory space can store variables of any type. When using it, you need to search all memory areas

• The strong type is allocated in the specified memory according to the variable type, and the type cannot be converted directly. When using it, go directly to the area of ​​that type to find the value.

So generally changing the variable type in a weakly typed language can be modified directly. . However, strongly typed languages ​​cannot be modified directly, so the concept of pointers in strongly typed languages ​​is particularly important. We do not directly use the data in the memory. We create a reference variable (pointer). If you want to modify it, directly modify the memory address pointed by the pointer. Can.

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