我是C ++的新手,我正在阅读Stroustrup的书,但我对一个类的运算符重载有问题。我有这3个文件:
我像往常一样有两个文件,在标题中我有定义:
#ifndef EQUATIONS_H
#define EQUATIONS_H
#include<vector>
namespace equations {
//solve second degree equation
class eqSecDeg {
private:
double a;
double b;
double c;
std::vector<double> solArray;
double getDelta(double a, double b, double c);
public:
eqSecDeg(const double valA, const double valB, const double valC);
double getDelta();
std::vector<double> getSolutions();
//thrown with the error
class EquationError {
private:
char* msg;
int error_number;
public:
char* getMsg() { return msg; }
EquationError(char* a = "Error.", int err = 0) {
msg = a;
error_number = err;
};
};
//std::ostream& operator << (const std::ostream& x, eqSecDeg& A);
// ^ is commented but it gives the error that it should be declared with only 1 parameter (?)
};
}
#endif
在这里你可以看到dqsecdegree.cpp的实现:
#include<math.h>
#include "dqsecdegree.h"
namespace equations {
double eqSecDeg::getDelta(double a, double b, double c) {
return (b*b)-(4*a*c);
}
double eqSecDeg::getDelta() {
return (b*b)-(4*a*c);
}
//constructor
eqSecDeg::eqSecDeg(const double valA, const double valB, const double valC) {
if (valA == 0) {
throw EquationError("Parameter 'a' cannot be zero.", 1);
}
a = valA;
b = valB;
c = valC;
}
std::vector<double> eqSecDeg::getSolutions() {
double delta = getDelta(a,b,c);
if (delta >= 0) {
//x1 real and complex
solArray.push_back( (-b+sqrt(delta))/(2*a) );
solArray.push_back(0);
//x2 real and complex
solArray.push_back( (-b-sqrt(delta))/(2*a) );
solArray.push_back(0);
} else {
delta *= -1;
//x1 real and complex
solArray.push_back( -b/(2*a) );
solArray.push_back( (sqrt(delta)/(2*a)) );
//x2 real and complex
solArray.push_back( -b/(2*a) );
solArray.push_back( -(sqrt(delta)/(2*a)) );
}
return solArray;
}
std::ostream& eqSecDeg::operator << (std::ostream& x, eqSecDeg& A) {
return x << "something here";
}
}
在SO和谷歌上有很多答案,但我找不到正确的答案。我试图了解如何使用运算符重载。 我想在头文件中声明运算符重载并在cpp上执行它的正确。
friend
关键字只提供对所有成员的访问权限,而不会使该方法成为该类的一部分。当我使用该关键字时,编译器告诉我没有int / double / char /的ostream输出的有效定义。 哪里我应该放置运算符重载定义吗?我无法理解我必须在哪里(以及如何)实现它。有什么建议吗?
不是很相关,但主要是这样的:
//a, b, c taken from the cin istream
equations::eqSecDeg solver(a,b,c);
std::vector<double> soluzioni = solver.getSolutions();
//here I'd like to call this
std::cout << solver;
答案 0 :(得分:1)
将该函数声明为.h文件中的非成员函数。
std::ostream& eqSecDeg::operator<<(std::ostream& x, eqSecDeg const& A);
像你一样在.cpp文件中实现该功能。更新它以使用const&
而不是非常量&
。
在任何您喜欢的地方使用它。
eqSecDeg A;
...
std::cout << A << std::endl;