What is the difference between declarations and definitions?

In C++, the terms "declaration" and "definition" have specific meanings that are crucial to understand when programming. A declaration introduces an identifier (such as a variable, function, or class) to the program, allowing the compiler to recognize it. However, it does not allocate memory or provide the complete implementation of the item. A definition, on the other hand, provides a full implementation and allocates memory for the variable or function. In essence, every definition is a declaration, but not every declaration is a definition.

For example:

// Declaration of a function void myFunction(); // Definition of a function void myFunction() { // Function implementation } // Declaration of a variable extern int myVar; // Definition of a variable int myVar = 10;

C++ declaration definition programming variables functions identifier

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