C++ · 3 · Memory & Smart Pointers12 / 36 · 33%

new, delete & Why You Should Avoid Them

The raw layer under smart pointers — know it, then stop writing it.

Examples: new, delete[], leaks, make_unique

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Raw Allocation

new calls the constructor; delete calls the destructor.

Example

example

Widget* w = new Widget(42);
delete w;

int* arr = new int[100];
delete[] arr;          // [] form is mandatory for arrays

objects on the heap outlive their scope

malloc vs new

They are not interchangeable.

malloc / free

aspect	behaviour
ctor/dtor	not called
return	void*
failure	returns NULL
size	you compute it

→

new / delete

aspect	behaviour
ctor/dtor	called
return	typed pointer
failure	throws bad_alloc
size	deduced

Never free() something from new, or delete something from malloc().

The Leak Paths

Any early return or throw between new and delete leaks.

Example

example

void bad() {
    Widget* w = new Widget;
    if (!validate()) return;   // LEAK
    risky();                   // throws -> LEAK
    delete w;
}

void good() {
    auto w = std::make_unique<Widget>();  // always freed
}

Modern Guidance

Almost no application code should contain new or delete.

TIP

Prefer a value member, then std::vector/std::string, then make_unique, then make_shared. Raw new belongs inside library internals only.