Modern C++ – Yes with lambdas!
In current versions of c++ (C++11, C++14, and C++17), you can have functions inside functions in the form of a lambda:
int main() {
// This declares a lambda, which can be called just like a function
auto print_message = [](std::string message)
{
std::cout << message << "\n";
};
// Prints "Hello!" 10 times
for(int i = 0; i < 10; i++) {
print_message("Hello!");
}
}
Lambdas can also modify local variables through **capture-by-reference*. With capture-by-reference, the lambda has access to all local variables declared in the lambda’s scope. It can modify and change them normally.
int main() {
int i = 0;
// Captures i by reference; increments it by one
auto addOne = [&] () {
i++;
};
while(i < 10) {
addOne(); //Add 1 to i
std::cout << i << "\n";
}
}
C++98 and C++03 – Not directly, but yes with static functions inside local classes
C++ doesn’t support that directly.
That said, you can have local classes, and they can have functions (non-static
or static
), so you can get this to some extend, albeit it’s a bit of a kludge:
int main() // it's int, dammit!
{
struct X { // struct's as good as class
static void a()
{
}
};
X::a();
return 0;
}
However, I’d question the praxis. Everyone knows (well, now that you do, anyway :)
) C++ doesn’t support local functions, so they are used to not having them. They are not used, however, to that kludge. I would spend quite a while on this code to make sure it’s really only there to allow local functions. Not good.