How is the scope of a variable defined in C++?

In C++, the scope of a variable refers to the region of the program where the variable is valid and can be accessed. This means that the determining factor for a variable's scope is based on where it can be referenced and used throughout the code.

For example, a variable declared within a function has a local scope and can only be accessed within that function. Conversely, a variable declared outside of any function or class has a global scope and can be accessed from any part of the program that follows its declaration. This concept is crucial for understanding how to manage and organize code effectively, as it helps prevent naming conflicts and ensures that variables are used in the intended context.

The other options do not accurately capture the definition of a variable's scope in C++. While the datatype determines the type of data the variable can hold and the function declaration might imply a local scope, these aspects do not define how accessibility is controlled. The name of the variable is simply an identifier and does not relate to the scope itself. Thus, focusing on where the variable can be accessed is the key aspect of understanding variable scope in C++.