How can we get the size of an array that is passed into the function?

Question

This is my program, can someone tell me how to get the right value of 'n'(which is size of array) here without passing it to function?

#include <iostream>
using namespace std;

char * findFrequency (int input1[],int input2)
{
    int n = sizeof(input1) / sizeof(input1[0]);
    
    int count = 0;
    for(int i = 0; i < n; i++)
    {
        if(input1[i] == input2) 
         count++;
    }
    string ch;
    if(count == 0) 
     ch = to_string(input2) + " not present"; 
    else 
     ch = to_string(input2) + " comes " + to_string(count) + " times";
    std::cout << ch << "\nn = " << n;
}
int main ()
{
    int a[] = {1, 1, 3, 4, 5, 6};
    findFrequency(a, 1);
}

You can't. This is one of many reasons why you should use a std::vector instead of an array. — john, Sep 30 '20 at 13:35
@vahancho That only works with proper arrays. It won't work with a pointer to the first element of an array, which is how array type function arguments are implemented. — François Andrieux, Sep 30 '20 at 13:35
@KAditi -- Please note that this: `char * findFrequency (int input1[],int input2)` is exactly the same as `char * findFrequency (int* input1,int input2)`, That is the reason why it is 2. `sizeof(int *) / sizeof(int)` — PaulMcKenzie, Sep 30 '20 at 13:48

Vasilij · Accepted Answer · 2020-09-30T13:50:42.940

Of course you can always use a template:

#include <iostream>
using namespace std;

template<typename T, std::size_t N>
void findFrequency (T(&input1)[N], int input2)
{
    // input1 is the array
    // N is the size of it

    //int n = sizeof(input1) / sizeof(input1[0]);

    int count = 0;
    for(int i = 0; i < N; i++)
    {
        if(input1[i] == input2)
         count++;
    }
    string ch;
    if(count == 0)
     ch = to_string(input2) + " not present";
    else
     ch = to_string(input2) + " comes " + to_string(count) + " times";
    std::cout << ch << "\nn = " << N;
}
int main ()
{
    int a[] = {1, 1, 3, 4, 5, 6};
    findFrequency(a, 1);
}

How can we get the size of an array that is passed into the function?

1 Answers1