c++ references array

Question

Hello, I wounder how i can make this code work?

#include <iostream>
using namespace std;

void writeTable(int (&tab)[],int x){
    for(int i=0;i<x;i++){
        cout << "Enter value " << i+1 <<endl;
        cin >> tab[i] ;
    }
}


int main(void){
    int howMany;
    cout << "How many elemets" << endl;
    cin >> howMany;

    int table[howMany];
    int (&ref)[howMany]=table;
    writeTable(ref,howMany);
    return 0;
}

And here are the errors that I have:

|4|error: parameter ‘tab’ includes reference to array of unknown bound ‘int []’|
|18|error: invalid initialization of reference of type ‘int (&)[]’ from expression of type ‘int [(((unsigned int)(((int)howMany) + -0x00000000000000001)) + 1)]’|
|4|error: in passing argument 1 of ‘void writeTable(int (&)[], int)’|

Thanks for help

Answer 1

If you are intending to pass the size of the array, then remove the reference

void f(int a[])

is equivalent to

void f(int* a)

so no copying will be done, if that is the concern.

If you want to take an array by reference, then you MUST specify the dimension. e.g.

void f(int (&a)[10])

Naturally, the best of the two is the third solution, which is to use std::vector's and pass them by reference, reference to const or by value if needed. HTH

Answer 2

Arrays of references are illegal, if that is what you are trying to do. It's not 100% clear to me from the title.

Answer 3

You need not specify the dimension of the array if you make writeTable a function template.

template <typename T,size_t N>
void writeTable(T (&tab)[N]) //Template argument deduction
{
    for(int i=0 ; i<N ; i++){
       // code ....
    }
}

.

int table[howMany]; // C++ doesn't have Variable Length Arrays. `howMany` must be a constant
writeTable(table);  // type and size of `table` is automatically deduced

Answer 4

Here is a slightly more C++ style of doing it:

#include <iostream>
#include <vector>

void writeTable(std::vector<int> &tab)
{
    int val;

    for (unsigned int i=0; i<tab.size(); i++)
    {
        std::cout << "Enter value " << i+1 << std::endl;
        if (std::cin >> val)
        {
            tab[i] = val;
        }
    }
}


int main()
{
    int howMany;
    std::cout << "How many elements?" << std::endl;
    std::cin >> howMany;

    std::vector<int> table(howMany);
    writeTable(table);

    return 0;
}