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20.7 Static Local Variables

The keyword static in a local variable declaration says to allocate the storage for the variable permanently, just like a file-scope variable, even if the declaration is within a function.

Here’s an example:

increment_counter ()
  static int counter = 0;
  return ++counter;

The scope of the name counter runs from the declaration to the end of the containing block, just like an automatic local variable, but its storage is permanent, so the value persists from one call to the next. As a result, each call to increment_counter returns a different, unique value.

The initial value of a static local variable has the same limitations as for file-scope variables: it can’t depend on the contents of storage or call any functions. It can use the address of a file-scope variable or a static local variable, because those addresses are determined before the program runs.