new and delete

Last reviewed May 28, 2026 Content v20260528

Track mode: server_compiled
Means: Compiled runner
Reading: ~1 min
Level: intermediate

This lesson

This lesson teaches new and delete: the syntax, patterns, and safety habits you need before advancing in C++.

Teams still ship new and delete in C++ codebases—skipping it leaves gaps in debugging and code reviews.

You will apply new and delete in contexts like: Game engines, trading systems, desktop apps, and performance-critical libraries.

Write C++ in main.cpp with int main(), click Run on server—the dev runner compiles with c++/g++ -std=c++17 -Wall and runs the binary; read template errors in stderr (LEARNING_RUNNER_ENABLED=true).

When you can explain the previous lesson's ideas without copying starter code.

new and delete allocate and release heap memory for single objects and arrays. They call constructors/destructors—unlike malloc/free in C.

Single object

int* p = new int(5);
delete p;
p = nullptr;

In modern C++, prefer std::make_unique and containers so cleanup is automatic.

Important interview questions and answers

Q: new vs malloc?
A: new invokes constructors and pairs with delete; malloc is C-style raw bytes.
Q: double delete?
A: Undefined behavior—set pointer to nullptr after delete or use smart pointers.

Self-check

What calls the destructor for heap objects?
Modern alternative to raw new/delete?

Pitfall: Every new needs matching delete (or array forms)—prefer std::make_unique so destructors run automatically.

Interview prep

new vs malloc?: new invokes constructors and pairs with delete; malloc allocates raw bytes in C style.
Double delete?: Undefined behavior—use smart pointers or set pointer to nullptr after delete.

Interview tip Lesson completion confidence

Can you explain this lesson in 30 seconds without reading notes?

Self-reflection (saved on this device)

Not saved yet.

Playground

Runs on the configured server runner (dev: npm run runner with LEARNING_RUNNER_ENABLED=true). Output appears below the editor.

Code runner not available

Server runner is disabled. Set LEARNING_RUNNER_ENABLED=true and LEARNING_RUNNER_URL in .env (see .env.example).

Check yourself

Multiple choice — immediate feedback.

Discussion

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new[] vs new?
Leak detect how?

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