Unlocking the Power of Variables in C++
When it comes to programming in C++, understanding variables is crucial. Every variable has two fundamental features: type and storage class. The type determines the kind of data that can be stored, such as integers, floats, or characters. On the other hand, the storage class controls two essential properties: lifetime and scope.
The Four Major Types of Variables
Depending on their storage class, variables can be categorized into four main types: local, global, static local, and register variables. Additionally, there’s thread local storage, a mechanism that allocates variables per thread.
Local Variables: Limited Scope, Temporary Existence
A variable defined within a function is called a local or automatic variable. Its scope is restricted to the function where it’s defined, and it ceases to exist when the function exits. For instance, in the example below, var cannot be used inside test(), and var1 cannot be used inside main().
Global Variables: Unlimited Scope, Permanent Existence
A variable defined outside all functions is a global variable, accessible throughout the program. Its life begins when the program starts and ends when the program terminates. In the example below, c is a global variable, visible to both main() and test() functions.
Static Local Variables: Persistent Value, Limited Scope
The static keyword specifies a static variable, which exists only within the function where it’s declared. Although its lifetime spans the entire program, its value persists between function calls. This is demonstrated in the example below, where var retains its value even after the function returns.
Register Variables: Faster, But Deprecated (C++11)
The register keyword, used for specifying register variables, was deprecated in C++11. These variables are similar to automatic variables, existing within a particular function only. However, they’re supposed to be faster since they’re stored in the processor’s register if available.
Thread Local Storage: One Instance per Thread
Thread-local storage allocates variables such that each thread has its own instance. This is achieved using the thread_local keyword. To learn more about thread local storage, explore beyond this introduction.
By grasping the differences between these variable types, you’ll unlock the full potential of C++ programming.