Question

Some C++ source code I wrote compiled and ran fine on Windows 7 using Visual Studio 2010. But when I tried it on Mac OS X 10.8 Mountain Lion using XCode 4.4.1, it would not compile. I was able to fix it as detailed below, but am interested to find out what I was doing wrong in the first place and why the fix was needed.

Specifically, consider the following class declaration:

class airline {
    vector <passenger> persons;
    int npassengers;
public:
    airline () {};
    airline (int np);
    ~airline () {};
    // other functions
} ;

The constructor for airline that takes an int parameter is:

airline::airline (int np) {
    npassengers = np;
    persons.resize (npassengers);
    return;
}

On the Windows machine, this compiled and ran with no problems. However, XCode complained bitterly that I did not have a viable constructor for “passenger”. I have a default constructor for passenger, so that wasn’t the issue. Based on something I found in an earlier question on this site I also tried using persons.erase instead of resize, with no luck.

Ultimately I was able to get the code to compile on the Mac by using persons.vector::resize (npassengers); instead of persons.resize (npassengers);. I am wondering why it was necessary to do that on the Mac side, and why it worked without a problem on the Windows side.

A related question is, is it bad practice to have using namespace std; at the top of your code, and instead, should I be specifying std::cout etc.? If so, why?

Please bear with my lack of knowledge, and thanks for your help!

Edit: Sean suggested I show my code for passenger, so here goes:

class passenger {
    string plast;
    string pfirst;
    int  row;
    char seatno;
    int flightno;
public:
    passenger ();
    passenger(string line );
    passenger (passenger const &rhs);
    ~passenger() {};
} ; 

passenger::passenger (passenger const &rhs) {
    plast = rhs.plast;
    pfirst = rhs.pfirst;
    row = rhs.row;
    seatno = rhs.seatno;
    flightno = rhs.flightno;

    return;
}

passenger::passenger( string line ) {
    // tokenizes string to obtain passenger data
    // seems to work fine, actual code is too long to include
    // and doesn't seem relevant here
}

passenger::passenger() {
    plast.clear();
    pfirst.clear();
    row = 0;
    seatno = '\0';
    flightno = 0;

    return;
}

Plus of course the usual accessors and overloaded insertion operator, etc. Thanks!

Answer 1

I cannot see any obvious reason why the code would not be portable, other than missing header files or problems with other code not shown in the question. I can suggest some lines of portable code with some improvements:

#include <vector>
#include "passenger.h" // assuming class passenger is declared here

class airline {
    std::vector <passenger> persons_; // trailing underscore to distinguish data members
public:
    airline () {};
    explicit airline (int np); // explicit constructor to avoid implicit conversion from int.
~airline () {};
// other functions
} ;

And in the .cpp file:

airline::airline (int np) : persons_(np) {} // persons has np passengers

You don’t need a separate data member for the number of passengers. You can get it from std::vector::size().