C++ Pointer array to set using STL begin and end

Question

I am learning C++ and stuck with one scenario where I have to convert array to set

I have pointer which holds the address of array and I want to get all unique elements of array into set . Using STL how its possible . Below is my code spinet and am also looking for good explanation .

#include<set>

void possiblepermutation(int *array) {
    set<int> roots(begin(array),end(array));

}

After reading below comment , I understood that as I am passing pointer so begin() and end() will have no idea about start and end . Can you help me what if I pass size of array along with array pointer , how to do.

void possiblepermutation(int *array , int n) {
        set<int> roots(begin(array),end(array)); // HOW TO THEN 

    }

You need the esize of the array, because any size information is lost when you pass an array to a function. — Rakete1111, Dec 29 '17 at 10:35
It isn't clear what your question is. But `array` is just a pointer, not an array. — juanchopanza, Dec 29 '17 at 10:35
Related/possible dupe: https://stackoverflow.com/questions/26909429/stdbegin-and-stdend-not-working-with-pointers-and-reference-why — Rakete1111, Dec 29 '17 at 10:36
When learning C++, you might find a [good book](https://stackoverflow.com/q/388242/1782465) handy. — Angew is no longer proud of SO, Dec 29 '17 at 10:46

Bathsheba · Accepted Answer · 2017-12-29T10:45:50.087

2

std::begin and std::end do not return the ranges of an array that has decayed to a pointer type. All they see is a pointer. Informally, they don't know that the pointer actually points to the first element in an array.

It's your job to either pass a C++ standard library container like a std::vector to your function, perhaps by reference, or pass the length of the array as a parameter: for example

void possiblepermutation(int* array , std::size_t n){
    std::set<int> roots(array, array + n);

edited Dec 29 '17 at 10:45

answered Dec 29 '17 at 10:36

Bathsheba

231,907
34
361
483

To the function, it is irrelevant if an array has decayed. All it knows is the parameter is a pointer. – juanchopanza Dec 29 '17 at 10:37
@juanchopanza: Indeed, that's what I'm trying to say. – Bathsheba Dec 29 '17 at 10:37
Updated question @Bathsheba – Sumeet Kumar Yadav Dec 29 '17 at 10:43
@Sumeet: Updated answer! – Bathsheba Dec 29 '17 at 10:44

C++ Pointer array to set using STL begin and end

1 Answers1