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

As other answers have mentioned, standard C and C++ do not permit you to define nested functions. (Some compilers might allow it as an extension, but I can't say I've seen it used).

You can declare another function inside a function so that it can be called, but the definition of that function must exist outside the current function:

#include 
#include 

int main( int argc, char* argv[])
{
    int foo(int x);

    /*     
    int bar(int x) {  // this can't be done
        return x;
    }
    */

    int a = 3;

    printf( "%d\n", foo(a));

    return 0;
}


int foo( int x) 
{
    return x+1;
}

A function declaration without an explicit 'linkage specifier' has an extern linkage. So while the declaration of the name foo in function main() is scoped to main(), it will link to the foo() function that is defined later in the file (or in a another file if that's where foo() is defined).