- Introduction to C++ pointers
- What is a void pointer?
- How to use pointers and arrays
- Return multiple values from a function using pointers?
- Dynamic arrays - How to create/change arrays at runtime?
- Two-dimensional dynamic array
- Function pointer
- Smart pointer
#includeWhat is a void pointer?using namespace std; int main() { int n = 5; cout << n << endl; cout << &n << endl; // address of n int *ptr = &n; cout << ptr << endl; cout << *ptr << endl; *ptr = 10; cout << *ptr << endl; cout << n << endl; // 10 int v; int *ptr2 = &v; *ptr2 = 6; // deference pointer cout << "v=" << v << endl; // 6 return 0; }
#includeHow to use pointers and arraysusing namespace std; void printNumber(int *numberPtr) { cout << *numberPtr << endl; } void printLetter(char *letterPtr) { cout << *letterPtr << endl; } // void pointer can point to any data type void print(void *ptr, char data_type) { switch (data_type) { case 'i': cout << *((int *) ptr) << endl; // cast void pointer into an int pointer break; case 'c': cout << *((char *) ptr) << endl; // be careful when using void pointer, compiler don't know you are making an error or not in this particular situation: // cout << *((float *) ptr) << endl; break; default: cout << *((double *) ptr) << endl; } } int main() { int number = 1; printNumber(&number); char letter = 'a'; printLetter(&letter); print(&number, 'i'); print(&letter, 'c'); return 0; }
#includeReturn multiple values from a function using pointers?using namespace std; void test1() { int luckyNumbers[5] = {1, 2, 3, 4, 5}; cout << &luckyNumbers[0] << endl; // 012FF704 // address of first element cout << &luckyNumbers[1] << endl; // 0083FD08 cout << &luckyNumbers[2] << endl; // 0083FD0C cout << endl; cout << luckyNumbers << endl; // 012FF704 // address of first element cout << luckyNumbers + 1 << endl; // 012FF708 cout << luckyNumbers + 2 << endl; // 012FF70C cout << endl; cout << *(luckyNumbers + 1) << endl; // 2 cout << *(luckyNumbers + 2) << endl; // 3 } int main() { // test1(); int luckyNumbers[5]; for (int i = 0; i < 5; ++i) { cout << "Number: "; cin >> luckyNumbers[i]; } for (int i = 0; i < 5; ++i) { cout << *(luckyNumbers + i) << " "; } }
#includeDynamic arrays - How to create/change arrays at runtime?using namespace std; int getMin(const int numbers[], int size) { int min = numbers[0]; for (int i = 1; i < size; ++i) { if (numbers[i] < min) { min = numbers[i]; } } return min; } int getMax(const int numbers[], int size) { int max = numbers[0]; for (int i = 1; i < size; ++i) { if (numbers[i] > max) { max = numbers[i]; } } return max; } // using pointer to return multiple value from a function void getMinMax(const int numbers[], int size, int *min, int *max) { for (int i = 1; i < size; ++i) { if (numbers[i] > *max) { *max = numbers[i]; } if (numbers[i] < *min) { *min = numbers[i]; } } } int main() { int numbers[5] = {1, 3, -2, 10, 28}; cout << "min is " << getMin(numbers, 5) << endl; cout << "max is " << getMax(numbers, 5) << endl; int min = numbers[0], max = numbers[0]; getMinMax(numbers, 5, &min, &max); cout << "min is " << min << " " << "max is " << max << endl; return 0; }
// Dynamic arrays #includeTwo-dimensional dynamic arrayusing namespace std; int main() { int size; cout << "Size: "; cin >> size; int *myArray = new int[size]; for (int i = 0; i < size; ++i) { cout << "myArray[" << i << "]: "; cin >> myArray[i]; } for (int i = 0; i < size; ++i) { // cout << myArray[i] << " "; cout << *(myArray + i) << " "; } delete[] myArray; // deallocate memory myArray = nullptr; return 0; }
#includeFunction pointerusing namespace std; int main() { int rows = 3, cols = 5; int **table = new int *[rows]; // pointer to pointer, create a new interger array of pointers for (int i = 0; i < rows; ++i) { // for each element, create a separate dynamic array table[i] = new int[cols]; } table[1][2] = 100; // access to elements on a specific position for (int i = 0; i < rows; ++i) { delete[] table[i]; } delete[] table; table = nullptr; }
#includeSmart pointer#include using namespace std; int getNumber() { return 5; } int add_two_num(int a, int b) { return a + b; } bool ascendingCompare(int a, int b) { return a < b; } bool decendingCompare(int a, int b) { return a > b; } void sortAscending(vector &numbersVector) { for (int i = 0; i < numbersVector.size(); ++i) { int bestIndex = i; for (int curIndex = i + 1; curIndex < numbersVector.size(); ++curIndex) { if (ascendingCompare(numbersVector[curIndex], numbersVector[bestIndex])) { bestIndex = curIndex; } } swap(numbersVector[i], numbersVector[bestIndex]); } } void sortDescending(vector &numbersVector) { for (int i = 0; i < numbersVector.size(); ++i) { int bestIndex = i; for (int curIndex = i + 1; curIndex < numbersVector.size(); ++curIndex) { if (decendingCompare(numbersVector[curIndex], numbersVector[bestIndex])) { bestIndex = curIndex; } } swap(numbersVector[i], numbersVector[bestIndex]); } } // use function pointer to optimize two functions above void customSort(vector &numbersVector, bool (*compareFunc)(int, int)) { for (int i = 0; i < numbersVector.size(); ++i) { int bestIndex = i; for (int curIndex = i + 1; curIndex < numbersVector.size(); ++curIndex) { if (compareFunc(numbersVector[curIndex], numbersVector[bestIndex])) { bestIndex = curIndex; } } swap(numbersVector[i], numbersVector[bestIndex]); } } void printNumber(const vector &numbersVector) { for (int i: numbersVector) { cout << i << " "; } cout << endl; } int main() { int (*funcPtr)() = getNumber; cout << funcPtr() << endl; int (*funcAdd)(int, int) = add_two_num; cout << funcAdd(3, 3) << endl; // compile error when lacking parameter // Cannot initialize a variable of type 'int (*)()' with an lvalue of type 'int (int, int)': different number of parameters (0 vs 2) // int (*funcAdd)() = add_two_num; vector myNumbers = {2, 5, 1, 3, 6, 4}; sortAscending(myNumbers); printNumber(myNumbers); vector myNumbers2 = {2, 5, 1, 3, 6, 4}; customSort(myNumbers2, ascendingCompare); printNumber(myNumbers2); // 1 2 3 4 5 6 customSort(myNumbers2, decendingCompare); printNumber(myNumbers2); // 6 5 4 3 2 1 return 0; }
#include#include using namespace std; void test_demo() { // create a unique pointer to an integer and assign value of 25 to address that unPtr1 is pointing to unique_ptr unPtr1 = make_unique (25); // cout << unPtr1 << endl; cout << *unPtr1 << endl; // unique_ptr unPtr2 = unPtr1; // error, can't assign a unique pointer to another unique pointer unique_ptr unPtr2 = move(unPtr1); cout << *unPtr2 << endl; // cout << *unPtr1 << endl; now, the pointer unPtr1 is empty, it's not pointer } class MyClass { public: MyClass() { cout << "Constructor invoked" << endl; } ~MyClass() { cout << "Destructor invoked" << endl; } }; void test_unique_pointer() { { unique_ptr unPtr1 = make_unique (); // Constructor invoked } // Destructor invoked } void test_shared_pointer() { shared_ptr sharedPtr1 = make_shared (); // shared_ptr {...} [1 strong ref] [make_shared] cout << sharedPtr1.use_count() << endl; // 1 { shared_ptr sharedPtr2 = sharedPtr1; cout << sharedPtr1.use_count() << endl; // 2 } cout << sharedPtr1.use_count() << endl; // 1 } void test_weak_pointer() { weak_ptr weakPtr1; { shared_ptr sharedPtr1 = make_shared (25); // shared_ptr 25 [1 strong ref] [make_shared] weakPtr1 = sharedPtr1; // value of weakPtr1 changes: // empty -> weak_ptr 25 [1 strong ref, 1 weak ref] [make_shared] -> expired [1 weak ref] [make_shared] } } int main() { // test_demo(); // test_unique_pointer(); // test_shared_pointer(); test_weak_pointer(); return 0; }
Video Tutorial Link：https://www.youtube.com/watch?v=kiUGf_Z08RQ&t=1746s
