Reading objects into an array from a text file with space delimiter - c++

Question

Good day,
I am trying to read data from a file into an array of objects. I can't seem to find how to tackle the space delimiter. Kindly help me.
The class is called Rational and it has two properties: num and denom.
File data: 1/2 -1/3 3/10 4/5 6/18
So far I have done this:
int operator>>(ifstream& fin, rational r[]) {
fin.open("filedata.txt", ios::in);
if (fin)
{
for (int i = 0; i < 5; i++)
{
fin >> r[i];
}
}
else
{
cout << "\nData file cannot be found!" << endl;
}
}
ifstream& operator>>(ifstream& in, rational& r)
{
int num, denom;
char slash;
in >> num >> slash >> denom;
r.set(num,denom);
return in;
}
Thanks in advance.

Answer 1

The function operator>>(ifstream& in, rational& r) should work as posted although I would change it to
std::istream& operator>>(std::istream& in, rational& r) { ... }
However, the first function is not right. You are not returning anything from the function even though its return type is int. You can change it to:
int operator>>(ifstream& fin, rational r[])
{
int count = 0;
fin.open("filedata.txt", ios::in);
if (fin)
{
for ( ; count < 5; ++count)
{
// If unable to read, break out of the loop.
if ( !(fin >> r[count] )
{
break;
}
}
}
else
{
cout << "\nData file cannot be found!" << endl;
}
return count;
}
Having said that, I think you can improve that function a bit.
Open the file in the calling function, main maybe, and pass the std::ifstream object to it.
Instead of passing it an array, pass it a std::vector. Then, you don't have worry about the number of entries in the file. You read whatever you can find in the file.
Change the return type to be std::istream& so you can chain the calls if necessary.
std::istream& operator>>(std::istream& in, std::vector<rational>& v)
{
rational r;
while ( in >> r )
{
v.push_back(r);
}
return in;
}
In main (or whichever is the higher level function), use:
std::vector<rational> v;
std::ifstream fin("filedata.txt);
if ( !fin )
{
// Deal with error.
}
else
{
fin >> v;
}
// Use v as you see fit.