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Display 116 Placing a Class in a Namespace (Header File)
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1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 //This is the header file dtimeh #ifndef DTIME_H A better version of this class definition will be #define DTIME_H given in Displays 118 and 119 #include <iostream> using std::istream; using std::ostream; namespace DTimeSavitch { class DigitalTime {
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<The definition of the class DigitalTime is the same as in Display 111>
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}; }// DTimeSavitch #endif //DTIME_H
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Note that the namespace DTimeSavitch spans two files The other is shown in Display 117
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Display 117 Placing a Class in a Namespace (Implementation File)
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1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 //This is the implementation file dtimecpp #include <iostream> #include <cctype> #include <cstdlib> using std::istream; You can use the single using directive using std::ostream; using namespace std; using std::cout; in place of these four using declarations using std::cin; However, the four using declarations are a #include "dtimeh"
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namespace DTimeSavitch {
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<All the function definitions from Display 112 go here>
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}// DTimeSavitch
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Separate Compilation and Namespaces
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compilation unit
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A compilation unit is a le, such as a class implementation le, along with all the les that are #included in the le, such as the interface header le for the class Every compilation unit has an unnamed namespace A namespace grouping for the unnamed namespace is written in the same way as for any other namespace, but no name is given, as in the following example:
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namespace { void sampleFunction( ) } //unnamed namespace
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All the names de ned in the unnamed namespace are local to the compilation unit, and so the names can be reused for something else outside the compilation unit For example, Displays 118 and 119 show a rewritten (and nal) version of the interface
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Display 118 Hiding the Helping Functions in a Namespace (Interface File) (part 1 of 2)
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1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 //This is the header file dtimeh //Values of this type are times of //notation, as in 9:30 for 9:30 AM #ifndef DTIME_H #define DTIME_H #include <iostream> using std::istream; using std::ostream; This is the interface for the class DigitalTime day The values are input and output in 24-hour and 14:45 for 2:45 PM
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This is our final version of the class DigitalTime This is the best version and the one you should use The implementation to use with this interface is given in Display 119
namespace DTimeSavitch { class DigitalTime { public: DigitalTime(int theHour, int theMinute); DigitalTime( ); //Initializes the time value to 0:00 (which is midnight) getHour( ) const; getMinute( ) const; void advance(int minutesAdded); //Changes the time to minutesAdded minutes later
Namespaces
Display 118 Hiding the Helping Functions in a Namespace (Interface File) (part 2 of 2)
21 22 23 24 25 26 27 28 29 30 31 32 33 void advance(int hoursAdded, int minutesAdded); //Changes the time to hoursAdded hours plus minutesAdded minutes later friend bool operator ==(const DigitalTime& time1, const DigitalTime& time2); friend istream& operator >>(istream& ins, DigitalTime& theObject); friend ostream& operator <<(ostream& outs, const DigitalTime& theObject); private: Note that the helping functions are not int hour; mentioned in the interface file int minute; }; } //DTimeSavitch #endif //DTIME_H
Display 119 Hiding the Helping Functions in a Namespace (Implementation File) (part 1 of 3)
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 //This is the implementation file dtimecpp of the class DigitalTime //The interface for the class DigitalTime is in the header file dtimeh #include <iostream> #include <cctype> #include <cstdlib> using std::istream; using std::ostream; using std::cout; using std::cin; #include "dtimeh" namespace { int digitToInt(char c) { return ( int(c) - int( 0 ) ); }
Specifies the unnamed namespace
Names defined in the unnamed namespace are local to the compilation unit So, these helping functions are local to the file dtimecpp
//Uses iostream, cctype, and cstdlib: void readMinute(int& theMinute) { char c1, c2; cin >> c1 >> c2; if (!(isdigit(c1) && isdigit(c2))) { cout << "Error: illegal input to readMinute\n";