My question is in regards to friend functions as well as overloading the << and >>. From my understanding I thought friend functions could (and should) access private member variables directly. However in the case I have here the compiler would only accept my .cxx file when I used "get" functions to obtain each private variable.
Here is my header file
class BigNum public: // CONSTRUCTORS and DESTRUCTORS BigNum(); BigNum(int num, size_t optional_base = 10); BigNum(const char strin[], size_t optional_base = 10); // MEMBER FUNCTIONS size_t get_digit(size_t index) const; size_t get_used() const; size_t get_capacity() const; size_t get_base() const; bool get_sign() const; // FRIEND FUNCTIONS friend std::ostream& operator<<(std::ostream &os, const BigNum &bignum); friend std::istream& operator>>(std::istream &is, BigNum &bignum); private: size_t base; size_t *digits; bool positive; size_t used; Here is my corresponding .cxx file with the implementations for the friend functions
#include "file.h" #include <cstdlib> #include <iostream> #include <string> #include <cstring> using namespace std; std::ostream& operator <<(std::ostream &os, const BigNum &bignum) { if (bignum.get_sign() == false) os << '-'; for (size_t i = 0; i < bignum.get_used(); ++i) os << bignum.get_digit(bignum.get_used() - i - 1); return os; } std::istream& operator >>(std::istream &is, BigNum &bignum) { for (size_t i = 0; i < bignum.get_used(); ++i) is >> bignum.digits[i]; return is; } So in this regard the above friend operators compiled correctly. However why is it that my operator >> can access one private variable directly (is >> bignum.digits[i]) but the rest of the private variables need to be retrieved by 'get functions'
Below, when I try to write the overload operators in this regard (how I thought friend functions should properly call private variables):
std::ostream& operator <<(std::ostream &os, const BigNum &bignum) { if (bignum.positive == false) os << '-'; for (size_t i = 0; i < bignum.used; ++i) os << bignum.digits[used - i - 1]; return os; } std::istream& operator >>(std::istream &is, BigNum &bignum) { for (size_t i = 0; i < bignum.used); ++i) is >> bignum.digits[i]; return is; } I obtain the following errors.
BigNum2.cxx: In function `std::ostream& csci2270_hw1B::operator<<(std::ostream&, const csci2270_hw1B::BigNum&)': BigNum2.cxx:201: error: `used' undeclared (first use this function) BigNum2.cxx:201: error: (Each undeclared identifier is reported only once for each function it appears in.) BigNum2.cxx: In function `std::istream& csci2270_hw1B::operator>>(std::istream&, csci2270_hw1B::BigNum&)': BigNum2.cxx:208: error: syntax error before `)' token The compiler I am using is g++ (Version 3.3.1). Any help is appreciated, thank you.
Revised:
I updated the code so the bignum object could access the private variables. I did the following to the friend operator overloading << and it compiled fine. Thanks for the comments, that was a rookie mistake.
std::ostream& operator <<(std::ostream &os, const BigNum &bignum) { if (bignum.positive == false) os << '-'; for (size_t i = 0; i < bignum.used; ++i) os << bignum.digits[bignum.used - i - 1]; return os; } However the compiler is still producing errors for the >> operator
BigNum2.cxx: In function std::istream& csci2270_hw1B::operator>>(std::istream&, csci2270_hw1B::BigNum&)': BigNum2.cxx:208: error: syntax error before)' token
The >> is supposed to read in a number and the private member variable 'used' is supposed to record the length of the array. I am still somewhat confused on why the compiler accepts
std::istream& operator >>(std::istream &is, BigNum &bignum) { for (size_t i = 0; i < bignum.get_used()); ++i) is >> bignum.digits[i]; return is; } as opposed to:
std::istream& operator >>(std::istream &is, BigNum &bignum) { for (size_t i = 0; i < bignum.used); ++i) is >> bignum.digits[i]; return is; } Any thoughts? thanks.
