John Davidson

Message:

Note: This is a reference question for dealing with variable scope in PHP. Please close any of the many questions fitting this pattern as a duplicate of this one.

What is "variable scope" in PHP? Are variables from one .php file accessible in another? Why do I sometimes get "undefined variable" errors?

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My Answer:
Variable scope refers to the visibility and accessibility of variables within a program. In PHP, there are four main variable scopes:

1. Local scope: Variables declared within a function are considered to have local scope and can only be accessed within that function.

2. Global scope: Variables declared outside of any function are considered to have global scope and can be accessed from anywhere within the program.

3. Static scope: Variables declared within a function with the static keyword retain their value between function calls and have scope within that function.

4. Superglobal scope: PHP provides several predefined variables, known as superglobals, that are accessible from anywhere in the program. Examples of superglobals include $_GET, $_POST, $_SESSION, and $_SERVER.

It is important to note that variables declared within a function do not have access to variables declared outside of that function, unless they are passed as arguments or accessed through the global keyword. Additionally, variables declared within nested functions have access to variables declared in their parent functions.