How to check if a data type is an array? (C++)

Question

So I am currently a student and have run into the following exercise: Write a function that prints the elements in an array. The array is sent to the function by argument. If this argument is not an array, an exception of type invalid_argument must be thrown. Test the function in the main() function.

So my code is currently as follows:

#include <iostream>
#include <exception>
#include <string>

using std::cin;
using std::cout;
using std::endl;
using std::invalid_argument;
using std::string;

template<class T>void printArray(T arr){
    try{
        arr.size();
    }
    catch(...){
        for (int i=0; i < sizeof(arr); i++){
            cout << arr[i] << endl;
        }
    }
    throw invalid_argument("Argument not of type array");
};

int main(){
    string arrChars[5] = {"1", "2", "3", "John", "5"};
    string s = "Jack";
    try{
        printArray(arrChars);
    }
    catch(invalid_argument &e){
        cout << "Error: " << e.what() << endl;
    }

    return 0;
}

This is after already trying other options such as:

template<class T>void printArray(T arr[]){
...
}

Which doesn't allow the program to run either as I cannot pass any arguments to the printArray() function that are not arrays.

My plan with the code is to swap out arrChars and s as the arguments to printArray() in order to determine success off the program.

Answer 1

If this argument is not an array, an exception of type invalid_argument must be thrown.

That's... a weird thing to want to do in C++. Typically, we'd go for "if this argument is not an array, the code should not compile." But hey, we can do that too. Just write one function overload that takes an array, and one that takes anything:

template <typename T, size_t N>
void printArray(const T (&arr)[N]) {
    // print array of size N here
}

template <typename T>
void printArray(const T& ) {
   throw invalid_argument("Argument not of type array");
}

Answer 2

Try something like this

#include <iostream>
#include <type_traits>
#include <stdexcept>
#include <vector>

template <class T>
void printArray( const T &a )
{
    if ( !std::is_array<T>::value ) throw std::invalid_argument("Argument not of type array");

    for ( const auto &x : a ) std::cout << x << std::endl;
}

int main()
{
    int a[] = { 0, 1, 2, 3, 4, 5, 6, 7, 8, 9 };
    std::vector<int> v = { 0, 1, 2, 3, 4, 5, 6, 7, 8, 9 };

    try
    {        
        printArray( a );
        printArray( v );
    }
    catch ( const std::invalid_argument &e )
    {
        std::cout << e.what() << std::endl;
    }        
}   

The program output is

0
1
2
3
4
5
6
7
8
9
Argument not of type array