C++11 Using "Range-based for loop" (for each) for dynamic array

Question

If I have a static array, I can do something like that:

int a[] = {1, 2, 3};
for (const auto x: a) {printf("%d\n", x);}

Can I do something similar when I have a pointer (int* b) and array size (N)?

I'd rather avoid defining my own begin() and end() functions.

I'd also prefer not using std::for_each, but it's an option.

Instead of a pointer and size as separate items, why not a std::vector? — Jerry Coffin
– Jerry Coffin, Commented Dec 6, 2014 at 18:47
No, because of a quirky detail about namespaces, and even if possible the loop wouldn't know the size of the dynamic array. Related: stackoverflow.com/questions/28242073/… — alfC
– alfC, Commented Jan 30, 2015 at 20:48

Columbo · Accepted Answer · 2014-12-06 18:49:29Z

6

Just use a container-like wrapper:

template <typename T>
struct Wrapper
{
    T* ptr;
    std::size_t length;
};

template <typename T>
Wrapper<T> make_wrapper(T* ptr, std::size_t len) {return {ptr, len};}

template <typename T>
T* begin(Wrapper<T> w) {return w.ptr;}

template <typename T>
T* end(Wrapper<T> w) {return begin(w) + w.length;}

Usage:

for (auto i : make_wrapper(a, sizeof a / sizeof *a))
    std::cout << i << ", ";**

Demo.

With C++1Z we will hopefully be able to use std::array_view instead.

answered Dec 6, 2014 at 18:49

Columbo

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1 Comment

user972014 Over a year ago

How will the array_view be used?

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