is it possible in C or C++ to create a function inside another?

Question

Could someone please tell me if this is possible in C or C++?

void fun_a();
//int fun_b();
...
main(){
   ...
   fun_a();
   ...
   int fun_b(){
     ...
            


        

Answer 1

You can nest a local class within a function, in which case the class will only be accessible to that function. You could then write your nested function as a member of the local class:

#include 

int f()
{
    class G
    {
    public:
        int operator()()
        {
            return 1;
        }
    } g;

    return g();
}

int main()
{
    std::cout << f() << std::endl;
}

Keep in mind, though, that you can't pass a function defined in a local class to an STL algorithm, such as sort().

int f()
{
    class G
    {
    public:
        bool operator()(int i, int j)
        {
            return false;
        }
    } g;

    std::vector v;

    std::sort(v.begin(), v.end(), g);  //  Fails to compile
}

The error that you would get from gcc is "test.cpp:18: error: no matching function for call to `sort(__gnu_cxx::__normal_iterator > >, __gnu_cxx::__normal_iterator > >, f()::G&)' "