C++ Find an int in an array

Question

So I've read other Stack posts about this, and they all suggest that I use find. I'm attempting this, but it doesn't work for me.

bool findInArray(int number, int array[]){
    // Finds if the number is in the array
    bool exists = find(begin(array), end(array), number) != end(array);
    return exists;

}

But I keep getting the following error:

error: no matching function for call to ‘begin(int*&)’

It's even the accepted answer here: How can I check if given int exists in array?

why do you pass an array pointer instead of an array as a parameter to 'findInArray'? — Meccano, Apr 04 '17 at 17:22
Because in your function you don't have an array, you have a *pointer*. — Some programmer dude, Apr 04 '17 at 17:23
I don't know why I left that there. I'd been trying all sorts of things and I missed that. I've edited to what it actually looks like. — Cory Madden, Apr 04 '17 at 17:27
In your example, `int array[]` has an unknown size, there is no way for `std::end` to know where the end of the array is. — François Andrieux, Apr 04 '17 at 17:29

score 8 · Accepted Answer · answered Apr 04 '17 at 17:21

8

You need a template:

template <std::size_t N>
bool findInArray(int number, const int (&array)[N]) {
  // Finds if the number is in the array
  return std::find(std::begin(array), std::end(array), number) != std::end(array);
}

You also need to pass the array by lvalue, since you cannot pass arrays by prvalue in C++, and instead the array would decay to a pointer to its first element, thereby losing the size information.

answered Apr 04 '17 at 17:21

Kerrek SB

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Thanks. This appears to be the answer, but I'm not familiar with templates yet. I'll read up on those. – Cory Madden Apr 04 '17 at 17:30

score 1 · Answer 2 · answered Apr 04 '17 at 17:44

In case you do not know template and looking for an other answer to this question, use STL algorithms.

#include<iostream>
#include<algorithm>

bool findInArray(int number, int array[], int size_array){
  int* p   = std::find(array, array+size_array, number);
  if (p != array+size_array) {
    return 1;
  } else {
   return 0;
}

And from main, you can call :

findInArray(5, a, sizeof(a)/sizeof(a[0]));

C++ Find an int in an array

2 Answers2