Nested functions are not allowed but why nested function prototypes are allowed? [C++]

Question

I was reading the linked question which leads me to ask this question.

Consider the following code

int main()
{
    string SomeString();
}
         


        

Answer 1

Your prototype is just 'Forward Declaration'. Please check out the Wikipedia article.

Basically, it tells the compiler "don't be alarmed if the label 'SomeFun' is used in this way". But your linker is what's responsible for finding the correct function body.

You can actually declare a bogus prototype, e.g. 'char SomeFun()' and use it all over your main. You will only get an error when your linker tries to find the body of your bogus function. But your compiler will be cool with it.

There are lots of benefits. You have to remember the function body is not always in the same source code file. It can be in a linked library.Also, that linked library may be have a specific 'link signature'.Use conditional defines you may even select the correct link signature at build time using your scoped prototypes.Although most people would use function pointers for that instead.

Hope this helps.