Is there any way to use foreach in pointers? For example
int numbers[] = {1,2,3,4};
for (int& n : numbers) {
n *= 2;
}
this works fine but if I change numbers with int pointer foreach gives error.
int* numbers = new int[4];
*numbers = 1;
*(numbers + 1) = 2;
*(numbers + 2) = 3;
*(numbers + 3) = 4;
for (int& n : numbers) {
n *= 2;
}
delete[] numbers;
Aren’t they both basically the same thing? I’m allocating 16 bytes of space for both, and it’s obvious where they’ll end up. Why does it work fine in the above example but not in the other example?
4
A range-based for loop only works on containers where the compiler can work out the container’s starting and ending iterators, either via:
-
non-static
begin()/end()methods -
overloads of the standalone
std::begin()/std::end()functions -
in the case of a fixed array, via pointer arithmetic using the array’s known size.
A pointer to an array does not satisfy that requirement. Although the pointer itself can act as the starting iterator, there is no way for the loop to know how many elements are in the array to determine its ending iterator.
So, you will have to use a traditional for loop instead:
int* numbers = new int[4];
numbers[0] = 1;
numbers[1] = 2;
numbers[2] = 3;
numbers[3] = 4;
for (int i = 0; i < 4; ++i) {
numbers[i] *= 2;
}
delete[] numbers;
Or, you can make your own iterators:
int* numbers = new int[4];
numbers[0] = 1;
numbers[1] = 2;
numbers[2] = 3;
numbers[3] = 4;
int *iter = numbers, *end = numbers + 4;
while (iter != end) {
*iter++ *= 2;
}
delete[] numbers;
0