How do I find the length of an array?

Question

Is there a way to find how many values an array has? Detecting whether or not I\'ve reached the end of an array would also work.

Answer 1

std::vector has a method size() which returns the number of elements in the vector.

(Yes, this is tongue-in-cheek answer)

Answer 2

Just a thought, but just decided to create a counter variable and store the array size in position [0]. I deleted most of the code I had in the function but you'll see after exiting the loop, prime[0] is assigned the final value of 'a'. I tried using vectors but VS Express 2013 didn't like that very much. Also make note that 'a' starts at one to avoid overwriting [0] and it's initialized in the beginning to avoid errors. I'm no expert, just thought I'd share.

int prime[] = {0};
int primes(int x, int y){
    using namespace std; int a = 1;
    for (int i = x; i <= y; i++){prime[a] = i; a++; }
    prime[0] = a; return 0;
}

Answer 3

Avoid using the type together with sizeof, as sizeof(array)/sizeof(char), suddenly gets corrupt if you change the type of the array.

In visual studio, you have the equivivalent if sizeof(array)/sizeof(*array). You can simply type _countof(array)

Answer 4

Lets say you have an global array declared at the top of the page

int global[] = { 1, 2, 3, 4 };

To find out how many elements are there (in c++) in the array type the following code:

sizeof(global) / 4;

The sizeof(NAME_OF_ARRAY) / 4 will give you back the number of elements for the given array name.

Answer 5

While this is an old question, it's worth updating the answer to C++17. In the standard library there is now the templated function std::size(), which returns the number of elements in both a std container or a C-style array. For example:

#include <iterator>

uint32_t data[] = {10, 20, 30, 40};
auto dataSize = std::size(data);
// dataSize == 4

Answer 6

you can find the length of an Array by following:

int  arr[] = {1, 2, 3, 4, 5, 6}; 
int size = *(&arr + 1) - arr; 
cout << "Number of elements in arr[] is "<< size; 
return 0;