我的问题是关于朋友的功能以及重载<<和>>从我的理解,我认为朋友的功能可以(并且应该)直接访问私有成员变量.但是在我这里的情况下,当我使用“get”函数来获取每个私有变量时,编译器将只接受我的.cxx文件.
这是我的头文件
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;
#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;
}
所以在这方面上面的朋友操作符编译正确.但是为什么我的运算符>>可以直接访问一个私有变量(是>> bignum.digits [i]),但是其余的私有变量需要通过’get函数’检索
下面,当我尝试在这方面编写重载操作符(我以为朋友的功能如何正确地调用私有变量)：
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;
}
我收到以下错误.
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
我使用的编译器是g(版本3.3.1).任何帮助不胜感激,谢谢.
修订：
我更新了代码,使得bignum对象可以访问私有变量.我对朋友的运算符进行了以下操作：<<它编译好了.感谢您的意见,那是新秀的错误.
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;
}
但是,编译器仍然会产生>>操作者
BigNum2.cxx：在函数std :: istream&
csci2270_hw1B :: operator>>(std :: istream& csci2270_hw1B :: BigNum&)’：
BigNum2.cxx：208：错误：之前的语法错误)’标记
>>应该读取一个数字,私有成员变量’used’应该记录数组的长度.我仍然对编译器接受的原因感到困惑
std::istream& operator >>(std::istream &is,BigNum &bignum)
{
for (size_t i = 0; i < bignum.get_used()); ++i)
is >> bignum.digits[i];
return is;
}
而不是：
std::istream& operator >>(std::istream &is,BigNum &bignum)
{
for (size_t i = 0; i < bignum.used); ++i)
is >> bignum.digits[i];
return is;
}
有什么想法吗？谢谢.
