ex18.15.16.17.cpp

/***************************************************************************
 *  @file       main.cpp
 *  @author     Queequeg
 *  @date       20  Nov 2014
 *  @remark     This code is for the exercises from C++ Primer 5th Edition
 *  @note
 ***************************************************************************/
//
// Exercise 18.15
// Explain the differences between using declarations and directives.
// This difference in scope between a using declaration and a using directive
// stems directly from how these two facilities work. In the case of a using
// declaration, we are simply making name directly accessible in the local
// scope. In contrast, a using directive makes the entire contents of a
// namespace available In general, a namespace might include definitions that
// cannot appear in a local scope. As a consequence, a using directive is
// treated as if it appeared in the nearest enclosing namespace scope.

// Exercise 18.16
// Explain the following code assuming using declarations for all the
// members of namespace Exercise are located at the location labeled
// position 1. What if they appear at position 2 instead? Now answer the
// same question but replace the using declarations with a using directive
// for namespace Exercise.

// Exercise 18.17
// Write code to test your answers to the previous question.


#include <iostream>
using std::cout;
using std::endl;

// using declarations for all the members of namespace Exercise
// are located at the location labeled position 1.
namespace Test0
{
	namespace Exercise
	{
		int ivar = 0;
		double dvar = 0;
		const int limit = 1000;
	}

	int ivar = 0;

	// using Exercise::ivar;
	// error C2874: using-declaration causes a multiple declaration of 'Test0::Exercise::ivar'
	// So we delete it to make the program compile.
	using Exercise::dvar;
	using Exercise::limit;

	void manip()
	{
		double dvar = 3.1416;

		cout << "********** Before call Test0::manip **********" << endl;
		cout << "Exercise::ivar " << Exercise::ivar << endl
			 << "Exercise::dvar " << Exercise::dvar << endl
		     << "Exercise::limit " << Exercise::limit <<endl
		     << "Test0::ivar " << Test0::ivar << endl
		     << "dvar in function manip" << dvar << endl;

		int iobj = limit + 1;  // Exercise::limit + 1
		++ivar;                // ++ Test0::ivar
		++Test0::ivar;         // ++ Test0::ivar

		cout << "********** After call Test0::manip  **********" << endl;
		cout << "Exercise::ivar " << Exercise::ivar << endl
			 << "Exercise::dvar " << Exercise::dvar << endl
		     << "Exercise::limit " << Exercise::limit <<endl
		     << "Test0::ivar " << Test0::ivar << endl
		     << "dvar in function manip " << dvar << endl
			 << "iboj in function manip " << iobj << endl;
	}
}


// using declarations for all the members of namespace Exercise
// are located at the location labeled position 2.
namespace Test1
{
	namespace Exercise
	{
		int ivar = 0;
		double dvar = 0;
		const int limit = 1000;
	}

	int ivar = 0;

	void manip()
	{
		using Exercise::ivar;
	    // using Exercise::dvar;
		// This using declaration causes a redefinition of Test1::Exercise::dvar.
	    // So we delete it to make the program compile.
	    using Exercise::limit;

		double dvar = 3.1416;

		cout << "********** Before call Test1::manip **********" << endl;
		cout << "Exercise::ivar " << Exercise::ivar << endl
			 << "Exercise::dvar " << Exercise::dvar << endl
		     << "Exercise::limit " << Exercise::limit <<endl
		     << "Test1::ivar " << Test1::ivar << endl
		     << "dvar in function manip" << dvar << endl;

		int iobj = limit + 1; // Exercise::limit + 1
		++ivar;               // ++ Exercise::ivar
		++Test1::ivar;        // ++ Test1::ivar

		cout << "********** After call Test1::manip  **********" << endl;
		cout << "Exercise::ivar " << Exercise::ivar << endl
			 << "Exercise::dvar " << Exercise::dvar << endl
		     << "Exercise::limit " << Exercise::limit <<endl
		     << "Test1::ivar " << Test1::ivar << endl
		     << "dvar in function manip " << dvar << endl
			 << "iboj in function manip " << iobj << endl;
	}
}

// using directive for namespace Exercise is located at the
// location labeled position 1.
namespace Test2
{
	namespace Exercise
	{
		int ivar = 0;
		double dvar = 0;
		const int limit = 1000;
	}

	int ivar = 0;

	using namespace Exercise;

	void manip()
	{
		double dvar = 3.1416;

		cout << "********** Before call Test2::manip **********" << endl;
		cout << "Exercise::ivar " << Exercise::ivar << endl
			 << "Exercise::dvar " << Exercise::dvar << endl
		     << "Exercise::limit " << Exercise::limit <<endl
		     << "Test2::ivar " << Test2::ivar << endl
		     << "dvar in function manip" << dvar << endl;

		int iobj = limit + 1; // Exercise::limit + 1
		// ++ivar;
		// error C2872: 'ivar' : ambiguous symbol
		// could be int Test2::ivar or int Test2::Exercise::ivar
		++Test2::ivar;        // ++ Test2::ivar

		cout << "********** After call Test2::manip  **********" << endl;
		cout << "Exercise::ivar " << Exercise::ivar << endl
			 << "Exercise::dvar " << Exercise::dvar << endl
		     << "Exercise::limit " << Exercise::limit <<endl
		     << "Test2::ivar " << Test2::ivar << endl
		     << "dvar in function manip " << dvar << endl
			 << "iboj in function manip " << iobj << endl;
	}
}

// using directive for namespace Exercise is located at the
// location labeled position 2.
namespace Test3
{
	namespace Exercise
	{
		int ivar = 0;
		double dvar = 0;
		const int limit = 1000;
	}

	int ivar = 0;

	void manip()
	{
		using namespace Exercise;

		double dvar = 3.1416;

		cout << "********** Before call Test3::manip **********" << endl;
		cout << "Exercise::ivar " << Exercise::ivar << endl
			 << "Exercise::dvar " << Exercise::dvar << endl
		     << "Exercise::limit " << Exercise::limit <<endl
		     << "Test3::ivar " << Test3::ivar << endl
		     << "dvar in function manip" << dvar << endl;

		int iobj = limit + 1; // Exercise::limit + 1
		// ++ivar;
		// error C2872: 'ivar' : ambiguous symbol
		// could be int Test3::ivar or int Test3::Exercise::ivar
		++Test3::ivar;        // ++ Test3::ivar

		cout << "********** After call Test3::manip  **********" << endl;
		cout << "Exercise::ivar " << Exercise::ivar << endl
			 << "Exercise::dvar " << Exercise::dvar << endl
		     << "Exercise::limit " << Exercise::limit <<endl
		     << "Test3::ivar " << Test3::ivar << endl
		     << "dvar in function manip " << dvar << endl
			 << "iboj in function manip " << iobj << endl;
	}
}

int main()
{
	Test0::manip();
	cout << endl;

	Test1::manip();
	cout << endl;

	Test2::manip();
	cout << endl;

	Test3::manip();
	cout << endl;

	return 0;
}