local array length is different from when it is called from a function

In the following code, std::extent<decltype(columns)>::value calculates the length of the given array. However, when the array is a function argument, the compiler behaves in different way. Could some one help me how to fix it?

output:

local array length: 5

function array length: 0

code:

#include <iostream>
#include <string>

void showcolumns_num(std::string columns[])
{
    int columns_num=std::extent<decltype(columns)>::value;
    std::cout<<"function array length: "<<columns_num<<std::endl;
}


int main()
{
    std::string column_list[]={"col1","col2","col3","col4","col5"};

    // local calculation of column number
    int columns_num=std::extent<decltype(column_list)>::value;
    std::cout<<"local array length: "<<columns_num<<std::endl;

    // function calculation of column number
    showcolumns_num(column_list);

    return 0;
}