Deep copy VS shallow copy

What is the difference between deep copy and shallow copy? Explain how you would use each.

A shallow copy copies all the member values from one object to another. A deep copy does all this and also deep copies any pointer objects.

An example of shallow and deep copy is below.

01 struct Test{
02   char* ptr;
03 };
05 void shallow_copy(Test& src, Test& dest){
06   dest.ptr=src.ptr;
07 }
09 void deep_copy(Test& src, Test& dest){
10   dest.ptr=malloc(strlen(src.ptr)+1);
11   memcpy(dest.ptr,src.ptr);
12 }
Note that shallow_copy may cause a lot of programming run time errors, especially with the creation and deletion of objects. Shallow copy should be used very carefully and only when a programmer really understands what he wants to do. In most cases, shallow copy is used when there is a need to pass information about a complex structure without actual duplication of data. One must also be careful with destruction of objects in a shallow copy.
In real life, shallow copy is rarely used. Deep copy should be used in most cases, especially when the size of the copied structure is small.
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