Where should function prototypes be declared?

Question

Where exactly should the prototypes be declared? For example right after the include statments, or right before the main method? I know they both compile but is one considered more standard or more redable?

#include <iostream>
#include <cstdlib>

const unsigned int PI = 3.14;

using namespace std;

int myFunc(int x, int y);
long factorial(int n);

int main()
{
  //...
  return 0;
}

or

#include <iostream>
#include <cstdlib>

int myFunc(int x, int y);
long factorial(int n);

using namespace std;



int main()
{
  //...
  return 0;
}

or shoudl they not be used at all and main should be declared last?

No one has really addressed if one way is more readable or prefered.

In your example, it doesn't make a difference. Somewhere before a function is actually called. — Igor Tandetnik, Oct 24 '14 at 04:01
Your two programs don't have any difference. You shouldn't be using `using namespace std` anyway. — Ryan, Oct 24 '14 at 04:02
i would suggest to put them in a header, and have main solo in that translation unit. — sp2danny, Oct 25 '14 at 09:10

score 1 · Answer 1 · edited May 23 '17 at 11:57

1

It would only matter if you actually used a type from the std in your function prototypes. In your example you don't, so it doesn't matter in your case.

This would not compile:

#include <string>

void foo(string const & s);

using namespace std;

But this would:

#include <string>

using namespace std;

void foo(string const & s);

But you shouldn't use using namespace std anyway.

edited May 23 '17 at 11:57

Community

1
1

answered Oct 24 '14 at 04:19

cdhowie

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score 0 · Answer 2 · answered Oct 24 '14 at 04:02

0

A function prototype must be declared before the function usage. It may be declared even in a block scope.

answered Oct 24 '14 at 04:02

Vlad from Moscow

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score 0 · Answer 3 · answered Oct 24 '14 at 04:02

In the example you have shown it doesn't matter.

The rule is:

A function has to be declared before you use it (in this case: call it).

Note: If the function is defined before its usage then you don't need explicit function declaration. The function definition serves the purpose.

Where should function prototypes be declared?

3 Answers3