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What Is a Copy Constructor?

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  • Written By: Alex Newth
  • Edited By: Angela B.
  • Last Modified Date: 09 November 2016
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    2003-2016
    Conjecture Corporation
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A copy constructor is a special function in C++, and other languages influenced by C++, that copies a coding object. The programmer does this by adding the copy constructor declaration and referencing an object. Primarily, this benefits the programmer by saving time, but it also ensures that the programmer does not enter the object’s coding incorrectly. When the copy is made, it must have a different memory pointer or it will point to the same section to which the original object is pointing. One of the major drawbacks of using copy constructors is that they cannot function independently; if the original object is erased, then the copy will be, as well.

When a programmer uses a copy constructor, he or she is telling the code to copy an object already listed in the code. To do this, the programmer must first use a declaration to tell the coding to perform the copy function. The programmer also must reference another object, so the object must already be built or there will be no way to perform the copy.

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The major benefit of using a copy constructor is that it saves time. Instead of having to retype the same functions and coding over again, the programmer can just add a reference and the object will be ready. This has another hidden benefit in consistent and accurate coding. As long as the original object is coded correctly, the copied object also will have the correct coding. Both of these benefits are most apparent with complex objects, but programmers also can benefit from copying simple objects.

In C++ languages, many functions require a memory pointer. This tells the function exactly where to look in the memory for certain information, or where it can store data. The programmer must specify a new memory pointer when a copy constructor is used; otherwise, the two objects will use the same memory space. On the surface, this may not seem bad, but it can lead to inconsistencies. For example, if both objects share the same pointer and one object is used to submit loan applications while the copied object is made to submit credit card applications, then all the credit card applications will be stored with the loan applications.

Programmers have to be wary of erasing an object, because copy constructor objects cannot function independently. If the programmer erases the original object, then the copied object will have nothing to reference. With no code to reference, the copied object will not be able to perform its task and will become useless.

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