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memory.cc
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Sat, Apr 26, 11:37

memory.cc
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#include <memory>
#include <vector>
#include <iostream>
void question1_stack() {
int values[10];
for (int& v : values)
v = 0;
for (int i = 0; i < 10; ++i)
std::cout << values[i] << " ";
std::cout << std::endl;
}
void question1_heap() {
int * values = new int[10];
// We can't use range-for with heap allocated arrays
// the best solution would use a std::vector
for (int i = 0; i < 10; ++i)
values[0] = 0;
for (int i = 0; i < 10; ++i)
std::cout << values[i] << " ";
std::cout << std::endl;
// The memory should be deallocated, otherwise we
// have a dangling pointer
delete[] values;
}
std::vector<int>* stack_allocation(int n) {
std::vector<int> values(n);
return &values; // good compilers show a warning here
}
std::vector<int>* heap_allocation(int n) {
std::vector<int>* values = new std::vector<int>(n);
return values;
}
void question2() {
std::vector<int> * stack_values = stack_allocation(10);
std::vector<int> * heap_values = heap_allocation(10);
// stack_values->size() should fail because memory was freed
// at the end of the function stack_allocation
std::cout << stack_values->size() << ", " << heap_values->size() << std::endl;
// We still need to delete
delete heap_values;
}
void question1_bis() {
std::array<int, 10> stack_values;
for (int& v : stack_values)
v = 0;
std::vector<int> heap_values(10);
for (int& v : heap_values)
v = 0;
// no need to delete, everything is managed
}
std::unique_ptr<std::vector<int>> unique_heap_allocation(int n) {
return std::make_unique<std::vector<int>>(n);
}
void question2_bis() {
std::unique_ptr<std::vector<int>> heap_vector = unique_heap_allocation(10);
std::cout << heap_vector->size() << std::endl;
// no need to delete: the unique pointer will deallocate everything at
// the end of the function
}
void question3() {
auto unique = std::make_unique<std::vector<int>>(10);
std::unique_ptr<std::vector<int>> other = nullptr;
// the move operation will make "unique" invalid
// so that there is ONLY ONE pointer to the resource
// hence "unique_ptr"
other = std::move(unique);
// memory will be deallocated nicely by the pointer "other"
}
void question3_bis() {
auto shared = std::make_shared<std::vector<int>>(10);
std::shared_ptr<std::vector<int>> other = nullptr;
// This works because they are shared pointer
other = shared;
// memory will be deallocated nicely
}
int main() {
question1_stack();
question1_heap();
//question2(); <-- this causes an error
question1_bis();
question2_bis();
question3();
question3_bis();
return 0;
}

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