ssrs gs1 128 Testing the Copy Constructor in Software

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EXAMPLE 10.4 Testing the Copy Constructor
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This test driver invokes the copy constructor twice: once when it initializes the object creator, and once when it initializes the object inventor:
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#include "String.h"
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main0 -C String name("Bjarne Stroustrup"); tout << "name = [I' <c name << "]\nn; String creator = name; // calls the copy constructor tout << "creator = [I' << creator c< "]\n"; String inventor = "Charles Babbage"; // calls two constructors tout << "inventor = [" c< inventor << "]\n";
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First it uses the third constructor to construct the String object name which duplicates the constant C-string "Bjarne Stroustrup". Then it uses the copy constructor to create the String object creator which duplicates the String object name by being initialized by it. The last declaration uses both constructors to construct the String object inventor. First it uses object that duplicates the constant C-string the third constructor to create a temporary String "Charles Babbage". Then it uses the copy constructor to create the String object inventor to duplicate the temporary object.
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A String CLASS
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10.5 THE ASSIGNMENT OPERATOR The assignment operator is used whenever one object is assigned to another object that has already been declared of the same class. Like the copy constructor, the assignment operator is automatically provided by the compiler if we don t write our own version. But it is unwise to rely upon the automatically generated assignment operator for classes whose objects contain pointers, because duplicating pointers does not duplicate the data to which they point.
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EXAMPLE 10.5 Using the Assignment Operator Generated by the Compiler
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This example shows what can go wrong when you rely upon the automatically generated assign-
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#include main0 String myCar = "Infiniti G20"; String yourCar = "Lexus ES3OO"; tout <c "\t myCar = [" c< myCar << "]\n"; tout << "\tyourCar = [" << yourCar << "]\n"; myCar = yourcar; // memberwise assignment tout << "After: myCar = yourCar\n"; tout << "\t myCar = [" << myCar << "]\n"; tout << "\tyourCar = [" <c yourCar << "]\n"; yourCar[6] = 'L'; tout << "After: yourCar[6] = 'L'\n"; tout << "\t myCar = [" c< myCar << "]\n"; tout << "\tyourCar = [" << yourCar << "]\n"; "String.h"
The assignment operator that is generated automatically by the compiler simply uses member-wise assignment. For our string class, that means that in the fifth statement in main ( > , yourcar. len is assigned to myCar. len and yourCar. buf is assigned to myCar. buf. But the buf members are pointers, so the result is that both yourcar. buf and myCar. buf point to the same C-string in memory: the one that contains Lexus ES3 0 0". So when you buy a new Lexus LS300, it becomes my car too! In other words, the assignment myCar = yourCar in this program means that I become a coowner of your new Lexus LS300 (and that I lost my Lexus ES300). The following diagram illustrates the problem:
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yourCar
yourCar memory:
myCar len
yourCarl lenm /
Both objects, yourcar and mycar, point to the same character string in memory. The assignment myCar = yourcar simply duplicated the integer len and the pointer buf, without duplicating the character string. So when the E" is changed to an L", it gets changed in both objects.
To overcome problems indicated by Example 10.5, we need to define our own assignment operator so that an assignment Y = x replaces the object Y with a duplicate of the object X. Here is our own assignment operator, defined explicitly:
String& String: :operator=(const String& -t if (&s == this) return *this; len = s.len; delete [] buf; buf = new char[s.len + 11; strcpy(buf, s.buf); return *this; s)
First it checks whether the object s is different from the object to which it is to be assigned. If they are already the same object, then nothing more needs to be done. The conditional tests whether the address of s is the same as the address (this) of the current object. If the two objects are not the same, then we recreate the current object so that it becomes a duplicate of S. After setting len to s . len, we deallocate the memory currently assigned to
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