Overload ifstream in c++ - c++

Question

I am trying to read complex numbers of the form x + y*i from a file which looks like this:
2 + 3i
4 + 5i
If I implement it like this it only works for the first line and I would like to be able to read again in the same manner the second line. Any ideas?
istream& operator>>(istream& in, Complex& c) {
in >> c.r >> c.i;
return in;
}

Answer 1

EDIT: Do not throw exceptions directly, as this is not the usual way of doing thing with iostreams.
EDIT: Process the sign character separately so that spaces in the input are allowed.
A quick and dirty solution:
istream& operator>>(istream& in, Complex& c)
{
char sign;
char suffix;
in >> c.r >> sign >> c.i >> suffix;
if ((sign != '+' && sign != '-') || suffix != 'i') {
in.setstate(ios::failbit);
}
if (sign == '-') {
c.i = -c.i;
}
return in;
}

Answer 2

You need to make sure that you read both the "+" and the "i" when processing the input.
The following implementation works:
struct complex
{
double r;
double i;
};
std::istream& operator>>(std::istream& in, complex& c)
{
char plus, i;
in >> c.r >> plus >> c.i >> i;
return in;
}
std::string initdata = "2 + 3i\n4 + 5i\n";
int main()
{
std::stringstream ss(initdata);
std::vector<complex> values;
std::istream_iterator<complex> begin(ss), end;
std::copy(begin, end, std::back_inserter<std::vector<complex>>(values));
}

Answer 3

I would do it like this :
#include <iostream>
struct complex
{
int r, i;
};
int main ()
{
complex co;
char c;
while ((std::cin >> co.r >> c /* '+' */ >> co.i >> c /* 'i' */))
{
std::cout << co.r << ' ' << co.i << "i\n";
}
}

Answer 4

This should work for you:
#include <iostream>
#include <sstream>
int main(int argc, char *argv[])
{
std::istringstream s(
"2 + 3i\n"
"4 + 5i\n"
);
char sgn;
double r;
double i;
while(s >> r >> sgn >> i) {
if(s.get() != 'i') {
std::cerr << "Missing i\n";
return -1;
}
std::cout << r << sgn << i << "i\n";
}
return 0;
}
Note: The space before the imaginary part and the trailing i are breaking the input.