无法从转换 <brace-enclosed initializer list> 到int（*）数组

Question

I am very new to C++, and would like some help with this error I keep getting.

#include <iostream>
#include <string>

using namespace std;

void print (int test[2][2]= {{1,2},{3,4}})
{
    cout << test[0][0] << endl;
    cout << test[1][0] << endl;
}

int main()
{
    print();
    return 0;
}

The error is: could not convert '{{1, 2}, {3, 4}}' from '' to 'int (*)[2]'|

I am a beginner in C++ and am still learning.

Answer 1

Function parameters declared as arrays are adjusted implicitly to pointers to their first elements.

So the function declaration actually looks like

void print ( int ( *test )[2] = { { 1, 2 }, { 3, 4 } } );

and the pointer may not be initialized such a way because it is a scalar object.

In fact these function declarations

void print( int test[10][2] );
void print( int test[2][2] );
void print( int test[][2] );
void print( int ( *test )[2] );

are equivalent and declare the same one function.

However you could define the parameter as a reference to an array. In this case you would get the expected result. For example

#include <iostream>

void print ( const int ( &test )[2][2] = { { 1, 2 }, { 3, 4 } } )
{
    std::cout << test[0][0] << std::endl;
    std::cout << test[1][0] << std::endl;
}


int main() 
{
    print();

    int a[2][2] = { { 5, 6 }, { 7, 8 } };

    print( a );
}    

The program output is

1
3
5
7

Answer 2

There is an easy work around:

void print (int test[2][2])
{
    cout << test[0][0] << endl;
    cout << test[1][0] << endl;
}
void print ()
{
    int test[2][2] = {{1,2},{3,4}};
    print(test);
}