When and How Are Function-Level Static Variables in C Allocated and Initialized?

Allocation and Initialization of Function-Level Static Variables

Function-level static variables in C are a type of data that persists throughout the lifetime of the program. Unlike global variables, they are not declared at the global scope, but rather within the scope of a function. This raises疑問 about when these variables are allocated and initialized.

In contrast to globally declared variables, which are allocated and initialized at the start of the program, function-level static variables are allocated and initialized upon the first call to the function in which they are defined. This is evident in the example code provided:

void doSomething() {
  static bool globalish = true;
}

The static variable globalish is initialized upon the first call to the function doSomething. Prior to that, its value is undefined. This result was confirmed through a test program that printed events related to the creation and destruction of objects instantiated within different scopes.

This behavior is attributed to the fact that static variables are stored in a static area of memory that is shared among all calls to the same function. Thus, the initial value remains persistent across calls, unless explicitly modified within the function.

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