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Nested Functions

6.4 Nested Functions

A nested function is a function defined inside another function. Nested functions are supported as an extension in GNU C, but are not supported by GNU C++.

The nested function's name is local to the block where it is defined. For example, here we define a nested function named square, and call it twice: 

foo (double a, double b)
{
  double square (double z) { return z * z; }

  return square (a) + square (b);
}

The nested function can access all the variables of the containing function that are visible at the point of its definition. This is called lexical scoping. For example, here we show a nested function which uses an inherited variable named offset: 

bar (int *array, int offset, int size)
{
  int access (int *array, int index)
    { return array[index + offset]; }
  int i;
  /* ...