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POShould '#include' and 'using' statements be repeated in both header and implementation files (C++)?
 

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  1. POShould '#include' and 'using' statements be repeated in both header and implementation files (C++)?
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    <p>I'm fairly new to C++, but my understanding is that a #include statement will essentially just dump the contents of the #included file into the location of that statement. This means that if I have a number of '#include' and 'using' statements in my header file, my implementation file can just #include the header file, and the compiler won't mind if I don't repeat the other statements.</p> <p>What about people though?</p> <p>My main concern is that if I don't repeat the '#include', 'using', and also 'typedef' (now that I think of it) statements, it takes that information away from the file in which it's used, which could lead to confusion.</p> <p>I am just working on small projects at the moment where it won't really cause any issues, but I can imagine that in larger projects with more people working on them it could become a significant issue.</p> <p>An example follows:</p> <p><strong>UPDATE:</strong> my function prototypes for 'Unit' have string, ostream and StringSet among their return types and parameters - I am not including anything in my header file that is used only in the implementation file.</p> <pre><code>//Unit.h #include &lt;string&gt; #include &lt;ostream&gt; #include "StringSet.h" using std::string; using std::ostream; class Unit { public: //public members with string, ostream and StringSet //in their return values/parameter lists private: //private members //unrelated side-question: should private members //even be included in the header file? } ; //Unit.cpp #include "Unit.h" //The following are all redundant from a compiler perspective: #include &lt;string&gt; #include &lt;ostream&gt; #include "StringSet.h" using std::string; using std::ostream; //implementation goes here </code></pre>
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    1. USDavid Mason
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    1. COAn unrelated question that I didn't want to clutter the main question with is, since everyone seems to say that global 'using' statements are a bad idea, how can I have just a class 'using std::string' or something? Moving that statement into the class declaration causes a compiler error because it doesn't like namespaces in a 'using' statement in that location.
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      1. USDavid Mason
    2. COWhat's wrong with explicitly saying `std::string`?
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      1. POShould '#include' and 'using' statements be repeated in both header and implementation files (C++)?
      1. USTravis Gockel
    3. COnothing much until it starts causing lines to break when they otherwise wouldn't, which reduces readability. Let's move away from std:: for a while though and say I wanted to make use of theLongestNamespeceNameInTheKnownUniverse::string - just to avoid the common 'you should always just type std::string' mantra (since I've heard it plenty of times already, and although a valid point it doesn't really help with the question at hand).
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