Why do functions need to be declared before they are used?

Question

When reading through some answers to this question, I started wondering why the compiler actually does need to know about a function when it first encounters it. Wo

Answer 1

I think of two reasons:

• It makes the parsing easy. No extra pass needed.
• It also defines scope; symbols/names are available only after its declaration. Means, if I declare a global variable int g_count;, the later code after this line can use it, but not the code before the line! Same argument for global functions.

As an example, consider this code:

void g(double)
{
    cout << "void g(double)" << endl;
}
void f()
{
    g(int());//this calls g(double) - because that is what is visible here
}
void g(int)
{
    cout << "void g(int)" << endl;
}
int main()
{
    f();
    g(int());//calls g(int) - because that is what is the best match!
}

Output:

void g(double)
void g(int)

See the output at ideone : http://www.ideone.com/EsK4A