C++ Things to note when using 'new' in constructors

Problems encountered when initializing pointer members of an object with new

When initializing pointer members using new in the constructor, the destructor must use delete, and new corresponds to delete, while new[] corresponds to delete[].

In the case of multiple constructors, it is necessary to use new in the same way, or not use new, or not use new[], because there is only one destructor, and all constructors must be compatible with the destructor.

PS. Of course, when initializing pointers with new in the constructor, you can initialize the pointer to be empty (0/NULL or C++11nullptr) because delete is compatible with null pointer whether it is with or without [].

You need to define a copy constructor and an assignment constructor yourself, and initialize one object to another object in the form of deep copy, as follows:

Copy constructor:

• Allocate enough space to store the copied data
• Copying data is not just an address
• Update the affected static class members

String:String(const String & st)
{
  num_Strings++;
  len = st.len;
  str = new char[len+1];
  std::strcpy(str, st.str());
}

Assignment constructor:

• Check for self-replication
• Release the member pointer before pointing to memory
• Copying data is not just an address
• Returns a reference to the calling object

String & String:operator=(const String & st)
{
  if(this == &st)
    return *this;
  else
    delete[] str;
    len = st.len;
    str = new char[len+1];
    std::strcpy(str, st.str());
  return *this;
}

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