C++ 当 符号重载 遇上 自定义类型转换 的 二义性解决（VS2019编译）

C++自定义类型数据（如复数）和普通类型数据做运算时，如果重载了‘+’号的同时，还自定义了类型转换，那么就可能遇到运算时二义性的问题；

运算符重载和自定义类型转换 如下

friend Complex  operator+(const Complex& c1, const Complex& c2);//重载‘+’号
operator double ()const ;//自定义类型转换Complex转double

二义性 解决--明确运算时数据的转换方式

      //类型转换 再加上 +号重载 运算会出现二义性，需要指明运算方式

	//运算方式一  转换为double
	f = 10.5 + (double)c + 'c';
	cout << "f=" << f << endl;


	//运算方式一  转换为Complex 结果再转换为 double
	f = (Complex)10.5 + c + (Complex)'c';
	cout << "f=" << f << endl;

先看运行结果：

f=23.5

f=133 //转为double的计算结果
f=133 //转为Complex的计算结果

n = 43

 

完整的程序

#define _CRT_SECURE_NO_WARNINGS
#include
#include
using namespace std;

class Complex
{
public:
	Complex(double real = 0.0, double imag = 0.0); 
	Complex& operator=(Complex& c);
	friend ostream & operator<<(ostream& out, Complex& c);
	friend Complex  operator+(const Complex& c1, const Complex& c2);//重载‘+’号
	operator double ()const ;//自定义类型转换Complex转double
private:
	double m_real;
	double m_imag;
};

void test01()
{
	Complex c1(20, 10);
	Complex c2(25.5);
	Complex c3 = c1;
	Complex c4 = Complex(100);
	Complex c5;
	
	cout << c1 << endl << c2 << endl << c3 << endl << c4 << endl << c5 <<  endl << endl;
}

void test02()
{
	//Complex c(23.5, 12.5);
	Complex c=Complex(23.5, 12.5);
	double f = c;
	cout << "f=" << f << endl;
	//类型转换 再加上 +号重载 运算会出现二义性，需要指明运算方式
	//运算方式一  转换为double
	f = 10.5 + (double)c + 'c';
	cout << "f=" << f << endl;
	//运算方式一  转换为Complex 结果再转换为 double
	f = (Complex)10.5 + c + (Complex)'c';
	cout << "f=" << f << endl;

	int n = Complex(43.2, 9.3);  //先转换为 double，再转换为 int
	cout << "n = " << n << endl;
}

int main()
{

	//test01();

	//cout << "=============================" << endl;

	test02();

	cout << endl;
	system("pause");
	return EXIT_SUCCESS;
}

Complex::Complex(double real, double imag):m_real(real), m_imag(imag)
{

}

Complex& Complex::operator=(Complex& c)
{
	this->m_real = c.m_real;
	this->m_imag = c.m_imag;
	return *this;
}

Complex  operator+(const Complex& c1, const Complex& c2)
{
	Complex tem;
	tem.m_real = c1.m_real + c2.m_real;
	tem.m_imag = c1.m_imag + c2.m_imag;
	
	return tem;
}

Complex::operator double () const
{
	return m_real;
}

ostream& operator<<(ostream& out, Complex& c)
{
	out << c.m_real << " + " << c.m_imag << "i";
	return out;
}

打开test01()和test02()的运行结果

20 + 10i
25.5 + 0i
20 + 10i
100 + 0i
0 + 0i

=============================
f=23.5
f=133
f=133
n = 43

总结一下：

当普通类型和复合类型数据定义了相互转化的方式，在进行两种类型数据运算时需要明确指出数据类型的转换方式，否则会出现二义性。