C++11 基于范围的异常错误

Question

I have been trying to learn The Revised C++11 and while trying a program with auto and nullptr using range-based for , I have a error: the program exits after accepting the first element of the array.

#include<iostream>

auto *Alloc(auto *p, int size) {
    if (p != nullptr)
        delete[]p;

    p = new auto[size];
    return p;
}

int main() {
    int *P = nullptr;
    Alloc(P, 5);

    for (auto &X : P)
        std::cin >> X;

    for (auto X : P)
        std::cout << X;

    std::cin.ignore(5);

    delete[]P;

    return 0;
}

Answer 1

P is not an array. It is defined as pointer.P

int *P=nullptr;

Pointers have no information about whether they point a separate single object or the first object of a sequence. There are no functions begin() and end() for pointers that are implicitly used in the range based for statement.

Take into account that instead of

int *P = nullptr;
Alloc(P, 5);

you have to write

int *P = nullptr;
P = Alloc(P, 5);

otherwise P will still be equal to nullptr.