How do I convert long doubles to char arrays? - c++

Question

I am running a C++ program to sort strings as numbers.
I am saving strings in a char array vector but want to sort numbers as numbers so I am converting number strings into long doubles by calling "tonum()" then converting them back to strings when I am done by calling "tostring()". I am calling "numstr()" strictly for readability and debugging. I convert numbers 0 through 7 and the 6th number across for each value changes every time I run it. In my actual program, the first 5 numbers also seem to change. How do I get consistent results for a long double so that I can properly sort long doubles in char arrays?
#include<iostream>
std::string::size_type sz;
//___________________________________________________
std::string tonum(std::string str)
{
const int len = sizeof(long double);
std::string out = "0000000000000000";
union
{
long double dbl;
char array[len];
};
try
{
dbl = stold(str);
}
catch(std::exception &err)
{
dbl = 0;
}
for (int i = 0; i < len; i++)
{
std::cout << (int)array[i] << "\n";
out[len-i-1] = array[i];
}
return(out);
}
//___________________________________________________
std::string fromnum(std::string str)
{
const int len = sizeof(long double);
std::string out = "";
union
{
long double dbl;
char array[len];
};
for (int i = 0; i < len; i++)
{
array[len-i-1] = str[i];
}
out = std::to_string(dbl);
return(out);
}
//_____________________________________________________
std::string numstr(std::string str)
{
std::string out = fromnum(str) + ":";
for (int i = 0; i < str.length(); i++)
{
std::string look = std::to_string(str[i]);
int lookint = stold(look,&sz);
if (lookint < 0) lookint += 256;
std::string look2 = std::to_string(lookint);
out += look2 + " ";
}
return(out);
}
//_____________________________________________________
int main()
{
std::cout << numstr(tonum("0")) << "\n";
std::cout << numstr(tonum("1")) << "\n";
std::cout << numstr(tonum("2")) << "\n";
std::cout << numstr(tonum("3")) << "\n";
std::cout << numstr(tonum("4")) << "\n";
std::cout << numstr(tonum("5")) << "\n";
std::cout << numstr(tonum("6")) << "\n";
std::cout << numstr(tonum("7")) << "\n";
}
//_____________________________________________________