How to convert a char* to a generic data type using one function only or/and an overload operator conversion?

Question

I have a template class Polinom, that uses generic data types(int, float, double, class Complex(defined by me)), and I want to convert a string to Polinom using this function for reading and a constructor:

Polion.cpp

 template<typename T> istream& operator>>(istream& in, Polinom<T>& P) { char line[1000]; in.getline(line, 1000); int gr = -1; T cf[100]; char* pt; pt = strtok(linie, " "); while (pt) { cf[++gr] = T(pt); pt = strtok(NULL, " "); } P = Polinom<T>(gr, cf); return in; }

Complex.cpp

 Complex::Complex(const char* str){ /* ... */ }

Everything is fine when I use Complex data type ( Polinom a(12, 4); std::cout << a << endl;) // I defined a friend ostream function for this line; ) because I write this constructor Complex::Complex(const char* str)

The problems appears when I use primitive data types

 Polinom<int> a(12, 4); because of T(const char* ) ===> int(const char*)

How can I solve this? Thank you very much!

Do you want your tokens to ONLY split on space ' '? Or is any whitespace appropriate for token splitting (en.cppreference.com/w/cpp/string/byte/isspace) — JohnFilleau
– JohnFilleau, Commented Mar 31, 2020 at 13:14

MSalters · Accepted Answer · 2020-03-31 13:06:33Z

0

This looks like you're reinventing the wheel. There's already a proper operator>> for int. You should add an overload for your Complex, so that in >> cf[gr++] compiles for every T.

answered Mar 31, 2020 at 13:06

MSalters

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1 Comment

Andrei Alexandru Dughila Over a year ago

I have already a proper operator >> for Complex, but I need one that works with Polionom<T> . Thank you!

Andrei Alexandru Dughila · Accepted Answer · 2020-03-31 21:06:10Z

I updated my code like this:

Polinom.cpp

 template<typename T> istream& operator>>(istream& in, Polinom<T>& P) { char linie[1000]; in.getline(linie, 1000); int gr = -1; T cf[100]; char* pt; pt = strtok(linie, " "); while (pt) { T a; string aux; try { aux = string(pt); if(aux.find("i") != string::npos) throw std::invalid_argument("invalid"); a = std::stod(pt); } catch(const std::invalid_argument& e){ cf[++gr] = (T)(pt); goto execute; } cf[++gr] = a; execute: pt = strtok(NULL, " "); } P = Polinom<T>(gr, cf); return in; } int main() { Polinom<Complex> a(12, 4); // it works std::cout << a << endl; Polinom<int> b; // it works std::cin >> b; std::cout << b; Polinom<double> c; // error C2440 'type cast': cannot convert from char* // to 'T' std::cin >> c; std::cout << c; return 0;

}

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