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C++ Tour Part III
Shared Pointer A shared pointer is a smart pointer that allows for distributed ownership of data. Each time it is assigned, a reference count is incremented, indicating one more owner of the data. When the pointer goes out of scope or an owner calls reset , the reference count is decremented. When the reference count goes to 0, the data pointed to is deallocated. Use make_shared : auto person = std :: make_shared < Person > ( ) ; if ( person ) { cout << "Person's address is " << person -> address ; } C++17 allows use of shared pointers to point to dynamically allocated arrays. However, make_shared cannot be used. Below is an example: shared_ptr < Person [ ] > persons ( new Person [ 10 ] ) ; persons [ 0 ] . _name = "Jack Sparrow" ; persons [ 0 ] . _address = "Caribbean" ; cout << "Address of first person " << persons [ 0 ] . address << endl ; A better solutio...
C++ strings and string_view
C-style strings C style strings should be avoided except when interfacing with C libraries. C string library functions provide no bounds checking and memory allocation support. They are represented as an array of characters. Last character of the string is the null character \0 , so that code that uses the string knows where it ends. The space needed for a string is always one more than the number of readable characters. String Literals Strings written with quotes around them are string literals. They are stored in a read-only part of memory. Because they are stored in readonly sections, attempting to modify string literals is undefined behavior . Example: char * str = "world" ; str [ 0 ] = 'y' ; //undefined behavior If the code respected the standard and assigned the string literal to const char* , the compiler will catch attempts to modify string literals: const char * str = "world" ; str [ 0 ] = 'k' ; //compiler will f...
Advanced Classes and Objects Part III
Part III Using swap When using moveFrom , if a new data member is added, both swap and moveFrom have to be modified. To avoid that, one can write the move constructor and move assignment operator with a default constructor and the swap function. class Bank { private : Bank ( ) = default ; } Now cleanup() and moveFrom() can be removed. The destructor handles the code from cleanup . The code is as follows: Bank :: Bank ( Bank && src ) noexcept : Bank ( ) { swap ( * this , src ) ; //Default constructor creates *this. } Bank & Bank :: operator = ( Bank && rhs ) noexcept { Bank temp ( std :: move ( rhs ) ) //Need std::move because rhs is named swap ( * this , temp ) ; return * this ; } Implementing swap with move semantics Using move semantics improves the performance of swap as seen below: void swa...
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