What\'s the Difference Between `static const` and `const` in C Data Members?

C Semantics of static const vs const

In C , the semantics of static const and const while introducing data members into a program may seem similar. However, there are subtle differences worth exploring.

Internal and External Linkage

When declaring a global variable outside a function, static const and const have no practical difference. Both variables will have internal linkage (visible only within the compilation unit) and static lifetime (lasting throughout the program's execution). However, static const may be preferred in C for consistency with global variables.

Inside Functions

Within a function, const allows for the declaration of a compile-time constant that cannot be changed during program execution. On the other hand, static const is used to create a static variable that retains its value throughout the function's lifetime, but can be computed from function parameters as it is not required to be a compile-time constant.

Inside Classes

For class members, static const refers to a constant that is initialized during program startup and remains constant throughout the program's runtime. In contrast, a non-static const member can be initialized in the constructor using an initializer list, allowing for dynamic initialization.

Read-Only vs. Constant

It is important to note that in C , const primarily denotes "read-only," not "constant." Hence, the value of a const variable can still be modified indirectly, such as through pointers.

These semantic differences highlight the functionality and flexibility of data members in C programming. Choosing the appropriate modifier (static const or const) depends on the specific requirements of the variable, including its scope, lifetime, and mutability.

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