Can C Functions Be Nested, and How Has This Evolved Across Different Standards?

Nested Functions in C

In the context of C , the question arises whether functions can be defined within other functions.

Modern C

In C 11 and later versions (C 14, C 17), nested functions are possible through the use of lambda expressions. Lambdas can be defined within functions and behave like anonymous functions:

int main() {
  auto print_message = [](std::string message) {
    std::cout << message << "\n";
  };

  for (int i = 0; i < 10; i++) {
    print_message("Hello!");
  }

  return 0;
}

C 98 and C 03

In C 98 and C 03, nested functions are not directly supported. However, a similar effect can be achieved through the use of local classes with static member functions:

int main() {
  struct X {
    static void a() {}
  };

  X::a();

  return 0;
}

While this approach provides a semblance of nested functions, it is not as straightforward as using lambdas in modern C .

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