c++ - 数组的引用作为返回值，为什么报错？

Question

初学者，但在网上找不到答案。。有哪位好心人能帮我看看，不甚感激

template<int SIZE> 
int(&a)[SIZE] insertSort(int(&arr)[SIZE])
{
    return arr;
};
void main()
{
    int arr[] = {2,4,56,65,3,6,9,4,3,5,8,4,2,1,0};
    insertSort(arr);//提示找不到insertSort函数，如果将函数的返回值修改一下，编译就能通过
}

Answer 1

There is also a problem with the way you write the function. I found an answer on stackoverflow. I can test it myself and run it

template<size_t n>
int (&insertSort(int (&arr)[n]))[n]
{
    return arr;
}

http://stackoverflow.com/a/2302395

By the way, try not to do this

1. This kind of code is difficult to read, and this template is not very scientific. A new n will generate a new function
2. If you want to return an array, you can use a pointer, but try not to do this, because allocating memory within a function can easily cause memory leaks (unless it only allocates memory)
3. The correct way to return an array is to pass a pointer to allocated memory, like thisvoid sort(const int *arr, int *sortedArr)
4. More recommendedvector

Answer 2

The first line is like this: template<int SIZE>

Answer 3

Since C++ is used, type safety can be achieved here without using pointers. As @wangdai said vector. As for returns, assignments, etc., you don’t have to worry about them. The simplest way is to use out参数

directly.

#include <vector>
#include <utility>
#include <iostream>

template<class t>
void insert_sorter(std::vector<t>& array /* out */) {
    /// ...
    array[3] = 0xff;
}

int main() {
    std::vector<int> array = {1, 2, 3, 4, 5};
    insert_sorter(array);
    std::cout << array.at(3) << std::endl;
}

Of course, if you have to go back to achieve the high-big effect, then do this

#include <vector>
#include <utility>
#include <iostream>

template<class t>
std::vector<t> insert_sorter(std::vector<t>& array) {
    /// ...
    array[3] = 0xff;

    /// move 语义不会重复拷贝array的data数据
    return std::move(array);
}

int main() {
    std::vector<int> array = {1, 2, 3, 4, 5};
    /// 这里使用了完美的移动赋值操作，是不是比`C`的方式顺眼多了
    /// 不过要记住array后面不能再使用了
    std::vector<int> ret = insert_sorter(array);
    std::cout << ret.at(3) << std::endl;
}

Honestly, the orthodox C++ way should be

/// 按stl的范式实现自己的sort
std::sort(s.begin(), s.end(), [](int a, int b) {
    return b < a;   
});