ex18.15.16.17

ch18/ex18.15.16.17/main.cpp

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+/***************************************************************************
+ *  @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;
+}