Helper function
C and C++ both have many helper functions which make it easier to work with memory, here are main ones explained:
new and delete operators:
new
: Allocates memory for a single objectdelete
: Deallocates memory for a single objectnew[]
: Allocates memory for an array of objectsdelete[]
: Deallocates memory for an array of objects
C-style memory management functions (from <cstdlib>):
malloc()
: Allocates a block of uninitialized memorycalloc()
: Allocates a block of zero-initialized memorymemset()
: Fills a block of memory with a specified value.memcpy()
:Copies a block of memory from a source to a destination.realloc()
: Reallocates a previously allocated memory blockfree()
: Deallocates a block of memory previously allocated by malloc, calloc, or realloc
Smart Pointers (from <memory>):
std::unique_ptr
: For exclusive ownership of dynamically allocated memorystd::shared_ptr
: For shared ownership of dynamically allocated memorystd::weak_ptr
: A weak reference to an object managed by std::shared_ptr
Allocator class (from <memory>):
std::allocator
: The default allocator used by standard containers
Other memory-related functions (from <memory>):
std::addressof()
: Obtains the actual address of an objectstd::align()
: Aligns pointer to the specified alignmentstd::uninitialized_copy()
: Copies a range of objects to uninitialized memorystd::uninitialized_fill()
: Fills a range of uninitialized memory with a valuestd::uninitialized_move()
: Moves a range of objects to uninitialized memorystd::destroy()
: Destroys objects in a range
C++17 additions:
std::launder()
: Helps deal with object lifetime issues in certain scenarios
C++20 additions:
std::make_unique_for_overwrite()
: Creates a unique_ptr without value-initializing its contentsstd::make_shared_for_overwrite()
: Creates a shared_ptr without value-initializing its contents
Placement new:
new (place_address) type
: Constructs an object at a specific memory address
It's worth noting that in modern C++, direct use of low-level memory management functions like malloc() and free() is generally discouraged in favor of C++-style memory management (new/delete) or, even better, smart pointers and standard containers.
The smart pointers (unique_ptr, shared_ptr, weak_ptr) are particularly important as they help manage memory automatically and prevent common issues like memory leaks and dangling pointers.
Example:
#include <iostream>
#include <cstdlib>
#include <memory>
#include <vector>
#include <cstring>
class MyClass {
public:
MyClass() { std::cout << "MyClass constructed\n"; }
~MyClass() { std::cout << "MyClass destructed\n"; }
};
int main() {
// 1. new and delete operators
std::cout << "1. new and delete operators:\n";
MyClass* ptr = new MyClass();
delete ptr;
int* arr = new int[5];
delete[] arr;
// 2. C-style memory management
std::cout << "\n2. C-style memory management:\n";
int* c_ptr = (int*)malloc(sizeof(int));
*c_ptr = 10;
std::cout << "malloc: " << *c_ptr << std::endl;
free(c_ptr);
int* c_arr = (int*)calloc(5, sizeof(int));
std::cout << "calloc: " << c_arr[0] << std::endl; // Will be 0
c_arr = (int*)realloc(c_arr, 10 * sizeof(int));
free(c_arr);
// memset with integers (be cautious!)
int numbers[5] = {1, 2, 3, 4, 5};
std::cout << "\nBefore memset: ";
for (int i = 0; i < 5; ++i) std::cout << numbers[i] << " ";
std::cout << std::endl;
memset(numbers, 0, sizeof(numbers));
std::cout << "After memset: ";
for (int i = 0; i < 5; ++i) std::cout << numbers[i] << " ";
std::cout << std::endl;
std::cout << "\nmemcpy example:\n";
char srcMemCpy[] = "Hello, memcpy!";
char destMemCpy[20];
memcpy(destMemCpy, src, strlen(srcMemCpy) + 1); // +1 to include null terminator
std::cout << "Source: " << srcMemCpy << std::endl;
std::cout << "Destination: " << destMemCpy << std::endl;
// 3. Smart Pointers
std::cout << "\n3. Smart Pointers:\n";
std::unique_ptr<MyClass> uptr = std::make_unique<MyClass>();
std::shared_ptr<MyClass> sptr = std::make_shared<MyClass>();
std::weak_ptr<MyClass> wptr = sptr;
// 4. Allocator
std::cout << "\n4. Allocator:\n";
std::allocator<int> alloc;
int* alloc_ptr = alloc.allocate(1);
alloc.construct(alloc_ptr, 42);
std::cout << "Allocator: " << *alloc_ptr << std::endl;
alloc.destroy(alloc_ptr);
alloc.deallocate(alloc_ptr, 1);
// 5. Other memory-related functions
std::cout << "\n5. Other memory-related functions:\n";
int x = 10;
int* addr = std::addressof(x);
std::cout << "addressof: " << addr << std::endl;
std::vector<int> src = {1, 2, 3, 4, 5};
std::vector<int> dest(5);
std::uninitialized_copy(src.begin(), src.end(), dest.begin());
std::cout << "uninitialized_copy: " << dest[2] << std::endl;
// 6. C++17 std::launder (usage is advanced and situational)
// Example omitted due to its specialized nature
// 7. C++20 additions
#if __cplusplus >= 202002L
std::cout << "\n7. C++20 additions:\n";
auto uptr_overwrite = std::make_unique_for_overwrite<int>();
auto sptr_overwrite = std::make_shared_for_overwrite<int>();
#endif
// 8. Placement new
std::cout << "\n8. Placement new:\n";
char memory[sizeof(MyClass)];
MyClass* placed_ptr = new (memory) MyClass();
placed_ptr->~MyClass(); // Call destructor manually
return 0;
}
Run it here.
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