reason for memory leakage in C C++

Question

what are the reasons for memory leakage in C C++ (except the usual allocating memory and forget to deallocate it)

Answer 1

If an exception is raised between allocation and deallocation, memory leak will occur.

void f1() {
    int* ptr = new int;

    // do something which may throw an exception

    // we never get here if an exception is thrown
    delete ptr;
}

Each time f1 terminates with an exception, 4 bytes are leaked (assuming int is 4 byte).