C++ Scope Rules

* In C++, scope rules in functions are governed by the concept of local scope and the lifetime of variables.

Scope Rules

Scope refers to the region of a program where a particular identifier, such as a variable or function, can be accessed or is valid. Scope rules help determine where in the code an identifier can be used and where it cannot. There are several types of scopes in C++:

Local Scope (Block Scope):

Variables declared inside a block of code (within curly braces '{}') have local scope. They are only accessible within that specific block and its nested blocks. Once the block is exited, the variables go out of scope and cannot be used.

void exampleFunction() {
    int x = 5; // x has local scope within this function
    // ...
}

Global Scope:

Variables declared outside of any function or block have global scope. They are accessible throughout the entire program. Global variables remain in scope for the entire program's execution.

// global variable
int globalVar = 20;

void exampleFunction() {
    // globalVar is accessible here
    // ...
}

⤏ Learn more about local & global variables with functions from the C language chapter.

Function Scope:

Parameters and local variables declared within a function have function scope. They are only accessible within that function.

void exampleFunction(int parameter) {
    // parameter has function scope
    int localVar = 10; // localVar also has function scope
    // ...
}

Class/Struct Scope:

Members of a class or struct have class scope. They are accessible within the class or struct and its member functions.

class MyClass {
public:
    int classVar; // classVar has class scope

    void memberFunction() {
        // classVar is accessible here
        // ...
    }
};

Namespace Scope:

Namespaces provide a way to organize code and avoid naming conflicts. Variables and functions declared within a namespace have namespace scope.

namespace MyNamespace {
    int x; // x has namespace scope

    void myFunction() {
        // x is accessible here
        // ...
    }
}

* It's important to note that C++ uses a concept called "name hiding" when dealing with nested scopes. If a variable in an inner scope has the same name as a variable in an outer scope, the inner variable "hides" the outer one within its scope. This is known as "shadowing."