Final answer:
Global variables declared outside of blocks in C and C++ have external linkage by default, making them accessible throughout the entire program or within the same file only, unless the 'extern' keyword is used for external access.
Step-by-step explanation:
In the context of programming languages such as Java and C++, variables declared outside of any function or block are typically referred to as global variables or static variables. These variables have global scope, which means they are accessible from any part of the program after their declaration. However, when we talk about the default class or storage class, for variables declared outside any block, they are considered to have external linkage by default in languages like C and C++. This means these variables are accessible in other files that are part of the program if they are declared with the 'extern' keyword. In contrast, in C++, a variable declared outside of a block without any explicit storage-class specifier has static storage duration and internal linkage, meaning it can only be accessed within the same file it is declared in unless specified otherwise with the 'extern' keyword.