Recursion in C function type with return

Question

This is a quick question, I did a search but couldn't find anything that answered my question.

When doing a recursive function in C do you need to have a return even when using a void function?

Eg:

    void addToLL(structA_ptr new, structA_ptr cur) {
        if (cur->next == NULL) {
             cur->next = new;
        } else {
          addToLL(new, cur->next);
        }
    }

Would I need to put a return keyword before the call to the function? I know that if the function would return something, like searching for something in the LL it would need a return statement.

Answer 1

No, you don't need it.

Long answer: Your recursive function is executed like any other and if doesn't encounter a recursive call, it is simply terminated. You don't need an explicit return. You can use if you want to exit the function prematurely.

Answer 2

There's no need for a return statement in this case, but only because the function doesn't do anything after the recursive call.

If you'd had this:

void addToLL(structA_ptr new, structA_ptr cur) {
    if (cur->next == NULL) {
         cur->next = new;
    } else {
         addToLL(new, cur->next);
    }

    someOtherCode();
}

then you'd need to insert a return; statement after the call to addToLL() if you didn't want someOtherCode() to be called after addToLL() returned.

Answer 3

Returning values from functions isn't a prerequisite for recursion - in any language. So, no.

Answer 4

It's more of a style issue. Some people consider ending a void function without a return keyword a faux-pas, others don't care. This really isn't recursion specific, though.

Answer 5

When your function ends, it implicitly returns, so there is no need to call the return instruction.

[Value Add] When functions are added returned in a program, the functions local variables and arguments are removed and return values are made available to the calling function, and execution resumes at the calling position.
When "void" functions are returned , they simply clean up arguments and local variables, and don't need to worry about moving return values to the right place.

Answer 6

There is no need for a return type.

A recursive function is still useful without a return type because it could for example print values, calculate things by pointer parameter, or do a variety of other things.

Answer 7

I believe your example code is a good example of a recursive function than can easily be converted to a loop making less strain on the stack when operating on a very long linked-list.

void addToLL(structA_ptr new, structA_ptr cur) {
    while (cur->next)
        cur = cur->next;
    cur->next = new;
}

Answer 8

In a function with return type of void the only reason to use an explicit return statement would be if you wanted to exit function prematurely.