C++ 从友元函数(运算符 <<)访问私有数组的元素
C++ Accessing an element of a private array from a friend function (operator <<)
我有一个 class 包含以下声明和随附的定义:
friend ostream& operator<<(ostream& out, const Poly& poly);
ostream& operator<<(ostream& out, const Poly& poly) {}
和
private:
int *polyArray;
在该运算符函数的代码中,我有(除其他外):
if (poly.polyArray[i] != 0) {
out << poly.polyArray[i];
}
我从编译器 (Visual Studio) 的下划线中得到以下错误消息,特别是在 "polyArray" 下方:
int *Poly::polyArray
Member "Poly::polyArray" is inaccessible
我可以很好地调用 public 成员函数,而且我认为我可以从友元函数访问私有数据成员。
关于我为什么会收到此错误的任何想法?
注意:
根据要求,以下是更多完整的 class:
首先是头文件。
class Poly
{
public:
Poly(int coeff, int expon);
friend ostream& operator<<(ostream& out, const Poly& poly);
private:
int *polyArray;
int size;
};
然后执行。
#include <iostream>
#include "Poly.h"
using namespace std;
Poly::Poly(int coeff, int expon) {
size = expon + 1;
polyArray = new int[size];
for (int i = 0; i < size; ++i) {
polyArray[i] = (i == expon ? coeff : 0);
}
}
ostream& operator<<(ostream& out, const Poly& poly) {
int currentSize = poly.getSize();
// If Poly is "empty", print 0
if (currentSize == 1 && poly.polyArray[0] == 0) {
out << 0;
return out;
}
for (int i = 0; i < currentSize; ++i) {
// Print the "+" sign if the coefficient is positive
//if (poly.polyArray[i] > 0) {
if (poly.polyArray[i] > 0) {
out << "+";
}
// Print the coefficient if it is not 0, skipping it and all following code otherwise
if (poly.polyArray[i] != 0) {
out << poly.polyArray[i];
}
else {
continue;
}
// Print "x" if the exponent is greater than 0
if (i > 0) {
out << "x";
}
// Print exponent if it is greater than 1
if (i > 1) {
out << "^" << i;
}
// Print a space if this is not the last term in the polynomial
if (i != currentSize - 1) {
out << " ";
}
}
return out;
}
最后,主要。
#include "Poly.h"
#include <iostream>
using namespace std;
int main() {
Poly y(5, 7);
cout << y;
return 0;
}
使用命名空间的指令(例如using namespace std
)仅适用于在该指令之后编写的代码和头文件。
在您的头文件 Poly.h
中,没有 ostream
的定义,因为 ostream
在名称空间 std 中。存在三种可能的修复方法:
using namespace std
在头文件中(不好的做法)
头文件中using std::ostream
使用std::ostream
的全名
friend std::ostream& operator<<(std::ostream& out, const Poly& poly);
如果我们应用第二个修复,这就是我们的文件现在的样子。
Poly.h
#include <iostream>
using std::ostream;
class Poly
{
public:
Poly(int coeff, int expon);
friend ostream& operator<<(ostream& out, const Poly& poly);
private:
int *polyArray;
int size;
};
Poly.cc
#include <iostream>
#include "Poly.h"
using namespace std;
Poly::Poly(int coeff, int expon) {
size = expon + 1;
polyArray = new int[size];
for (int i = 0; i < size; ++i) {
polyArray[i] = (i == expon ? coeff : 0);
}
}
ostream& operator<<(ostream& out, const Poly& poly) {
int currentSize = poly.getSize();
// If Poly is "empty", print 0
if (currentSize == 1 && poly.polyArray[0] == 0) {
out << 0;
return out;
}
for (int i = 0; i < currentSize; ++i) {
// Print the "+" sign if the coefficient is positive
//if (poly.polyArray[i] > 0) {
if (poly.polyArray[i] > 0) {
out << "+";
}
// Print the coefficient if it is not 0, skipping it and all following code otherwise
if (poly.polyArray[i] != 0) {
out << poly.polyArray[i];
}
else {
continue;
}
// Print "x" if the exponent is greater than 0
if (i > 0) {
out << "x";
}
// Print exponent if it is greater than 1
if (i > 1) {
out << "^" << i;
}
// Print a space if this is not the last term in the polynomial
if (i != currentSize - 1) {
out << " ";
}
}
return out;
}
main.cc
#include <iostream>
#include "Poly.h"
using namespace std;
int main() {
Poly y(5, 7);
cout << y;
return 0;
}
我有一个 class 包含以下声明和随附的定义:
friend ostream& operator<<(ostream& out, const Poly& poly);
ostream& operator<<(ostream& out, const Poly& poly) {}
和
private:
int *polyArray;
在该运算符函数的代码中,我有(除其他外):
if (poly.polyArray[i] != 0) {
out << poly.polyArray[i];
}
我从编译器 (Visual Studio) 的下划线中得到以下错误消息,特别是在 "polyArray" 下方:
int *Poly::polyArray
Member "Poly::polyArray" is inaccessible
我可以很好地调用 public 成员函数,而且我认为我可以从友元函数访问私有数据成员。
关于我为什么会收到此错误的任何想法?
注意: 根据要求,以下是更多完整的 class:
首先是头文件。
class Poly
{
public:
Poly(int coeff, int expon);
friend ostream& operator<<(ostream& out, const Poly& poly);
private:
int *polyArray;
int size;
};
然后执行。
#include <iostream>
#include "Poly.h"
using namespace std;
Poly::Poly(int coeff, int expon) {
size = expon + 1;
polyArray = new int[size];
for (int i = 0; i < size; ++i) {
polyArray[i] = (i == expon ? coeff : 0);
}
}
ostream& operator<<(ostream& out, const Poly& poly) {
int currentSize = poly.getSize();
// If Poly is "empty", print 0
if (currentSize == 1 && poly.polyArray[0] == 0) {
out << 0;
return out;
}
for (int i = 0; i < currentSize; ++i) {
// Print the "+" sign if the coefficient is positive
//if (poly.polyArray[i] > 0) {
if (poly.polyArray[i] > 0) {
out << "+";
}
// Print the coefficient if it is not 0, skipping it and all following code otherwise
if (poly.polyArray[i] != 0) {
out << poly.polyArray[i];
}
else {
continue;
}
// Print "x" if the exponent is greater than 0
if (i > 0) {
out << "x";
}
// Print exponent if it is greater than 1
if (i > 1) {
out << "^" << i;
}
// Print a space if this is not the last term in the polynomial
if (i != currentSize - 1) {
out << " ";
}
}
return out;
}
最后,主要。
#include "Poly.h"
#include <iostream>
using namespace std;
int main() {
Poly y(5, 7);
cout << y;
return 0;
}
使用命名空间的指令(例如using namespace std
)仅适用于在该指令之后编写的代码和头文件。
在您的头文件 Poly.h
中,没有 ostream
的定义,因为 ostream
在名称空间 std 中。存在三种可能的修复方法:
using namespace std
在头文件中(不好的做法)
头文件中using std::ostream
使用
std::ostream
的全名friend std::ostream& operator<<(std::ostream& out, const Poly& poly);
如果我们应用第二个修复,这就是我们的文件现在的样子。
Poly.h
#include <iostream>
using std::ostream;
class Poly
{
public:
Poly(int coeff, int expon);
friend ostream& operator<<(ostream& out, const Poly& poly);
private:
int *polyArray;
int size;
};
Poly.cc
#include <iostream>
#include "Poly.h"
using namespace std;
Poly::Poly(int coeff, int expon) {
size = expon + 1;
polyArray = new int[size];
for (int i = 0; i < size; ++i) {
polyArray[i] = (i == expon ? coeff : 0);
}
}
ostream& operator<<(ostream& out, const Poly& poly) {
int currentSize = poly.getSize();
// If Poly is "empty", print 0
if (currentSize == 1 && poly.polyArray[0] == 0) {
out << 0;
return out;
}
for (int i = 0; i < currentSize; ++i) {
// Print the "+" sign if the coefficient is positive
//if (poly.polyArray[i] > 0) {
if (poly.polyArray[i] > 0) {
out << "+";
}
// Print the coefficient if it is not 0, skipping it and all following code otherwise
if (poly.polyArray[i] != 0) {
out << poly.polyArray[i];
}
else {
continue;
}
// Print "x" if the exponent is greater than 0
if (i > 0) {
out << "x";
}
// Print exponent if it is greater than 1
if (i > 1) {
out << "^" << i;
}
// Print a space if this is not the last term in the polynomial
if (i != currentSize - 1) {
out << " ";
}
}
return out;
}
main.cc
#include <iostream>
#include "Poly.h"
using namespace std;
int main() {
Poly y(5, 7);
cout << y;
return 0;
}