Re: Header file question

From:

Victor Bazarov <v.bazarov@comcast.invalid>

Newsgroups:

comp.lang.c++

Date:

Wed, 25 Mar 2015 11:48:32 -0400

Message-ID:

<meulat$ugo$1@dont-email.me>

On 3/25/2015 9:46 AM, Joseph Hesse wrote:

The following 3 file program was constructed so I could get advice with
header file inclusion. The program compiles and run fine.

= Funcs.h =============================
#ifndef FUNCS_H
#define FUNCS_H

#include <vector>

double sum(std::vector<double> &vd);

#endif
= Funcs.cpp ===========================
#include "Funcs.h"

double sum(std::vector<double> &vd)
{
   double s = 0.0;

   for(const double &d : vd)
     s += d;

   return s;
}
= Test.cpp ============================
#include <iostream>
#include "Funcs.h"

int main()
{
   std::vector<double> numbers = {1.5, 2.5, 3.5, 4.5};

   std::cout << "The sum is " << sum(numbers) << std::endl;

   return 0;
}
=======================================

1. In Funcs.cpp the file Funcs.h was included since it seems like best
practices for an X.cpp to always include an X.h. However one could
argue that someone reading Funcs.cpp would see the use of the type
vector<double> and therefore #include <vector> should also be there,
even though it is redundant.

Every translation unit should include all headers that it needs to be
understood when read by a human being. Imagine that instead of the
standard container you would use some custom one, from some other
library. I think that in that case you would need to include the header
that defines that class/template. Same should apply to all standard
headers, I believe.

2. Same question for Test.cpp. Should #include <vector> be there since
it already comes from #include Funcs.h?

Yes. Same reason as before.

V
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