123 lines
2.5 KiB
C++
123 lines
2.5 KiB
C++
#include <iostream>
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#include <memory> // smart pointer header
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using namespace std;
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void changeInteger(int n);
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void changeIntegerPerPointer(int* pN);
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int changeIntegerPerReturn(int n);
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void changeIntegerPerReference(int& n);
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bool createInteger(int* pN);
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bool createIntegerWithPointerPointer(int** ppN);
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int main()
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{
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// general
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int* pNumber = nullptr;
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pNumber = new int(0);
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cout << "size of pNumber: " << sizeof(pNumber) << endl;
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cout << "size of pNumber data: " << sizeof(*pNumber) << endl;
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*pNumber = 567;
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// pNumber = new int(0); // BAD BAD - Memory Leak, because we override an existing pointer address with a new one without saving the old one
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// here are 100s of lines of code
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if (pNumber != nullptr)
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{
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delete pNumber;
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pNumber = nullptr;
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}
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// pointer as references
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//int number = 0;
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//changeInteger(number);
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//changeIntegerPerPointer(&number);
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//changeIntegerPerPointer(pNumber);
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//changeIntegerPerReference(number);
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// smart pointer
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// unique_ptr -> only one owner exist for the object
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// shared_ptr -> can have multiple owners
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// weak_ptr -> is loose connection to a shared_ptr
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unique_ptr<int> number = make_unique<int>(10);
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*number = 100;
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//unique_ptr<int> number2 = number; // compiler error - you can create a copy of an unique pointer
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unique_ptr<int> number2 = make_unique<int>(*number);
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shared_ptr<int> number3 = make_shared<int>(20);
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shared_ptr<int> number4 = number3;
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*number3 = 200;
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*number4 = 2000;
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number3.reset();
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weak_ptr<int> weakNumber = number4;
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//*weakNumber = 20000; // compiler error, weak pointer have no direct access to a shared pointer, you have to create one
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if (!weakNumber.expired())
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{
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shared_ptr<int> tmpSharedNumber = weakNumber.lock();
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*tmpSharedNumber = 20000;
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}
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number4.reset();
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shared_ptr<int> tmpSharedNumber = weakNumber.lock();
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// pointer-pointer
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if (createInteger(pNumber))
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{
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cout << "Create integer was succesful" << endl;
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}
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if (createIntegerWithPointerPointer(&pNumber))
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{
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cout << "Create integer was succesful" << endl;
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}
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if (pNumber != nullptr)
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{
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delete pNumber;
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pNumber = nullptr;
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}
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return 0;
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}
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void changeInteger(int n)
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{
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n = 100;
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}
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void changeIntegerPerPointer(int* pN)
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{
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cout << "address of pN: " << &pN << endl;
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if (pN == nullptr) return; // BE CAREFUL - if you don't what you get, do a test before
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*pN = 200;
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}
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void changeIntegerPerReference(int& n)
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{
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n = 300;
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}
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bool createInteger(int* pN)
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{
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pN = new int(0); // CAUTION - creates a MEMORY LEAK
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return false;
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}
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bool createIntegerWithPointerPointer(int** ppN)
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{
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*ppN = new int(0);
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return true;
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}
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