How Long Do Static Variables in C Function Scope Live?

The Lifetime of Static Variables in C Function Scope

Within a function, static variables declared with the static keyword exhibit a unique behavior compared to regular local variables. Understanding their lifetime is crucial for proper resource management and program execution.

Lifetime and Initialization

The lifetime of a static variable in a C function spans the entire execution of the program, from the point of declaration until program termination. This differs from regular local variables, which exist only within the scope of a single function call.

Static variables are initialized only once, the first time the program encounters the declaration. They retain their initialized value throughout subsequent function calls.

Constructor and Destructor Invocations

The constructor for a static variable is called only once, when the program first encounters the declaration. This occurs before any function calls that use the variable. The destructor for a static variable is also called when the program terminates, ensuring proper cleanup of any allocated resources.

Example

Consider the following code snippet:

void foo() 
{ 
    static string plonk = "When will I die?";
}

The static variable plonk is initialized once with the value "When will I die?" and retains this value throughout the program's execution. Its constructor is called only once, before the first call to foo(), and its destructor is called when the program terminates.

Implications for Multithreading

In multithreaded environments, the behavior of static variables can become more complex. While the standard does not specify how initialization and destruction of statics will be handled in the presence of multiple threads, this can be a potential point of contention. Proper synchronization mechanisms should be considered to avoid race conditions.

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