Explicit Sepcifier

最新推荐文章于 2024-09-18 08:35:22 发布

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本文探讨了显式指定符（Explicit Specifier）在编程中的作用，特别是在转换构造函数中的影响。首先，解释了转换构造函数如何允许隐式类型转换，例如将两个double数值转化为复数对象，或者单个double数值进行转化。接着，指出通过在构造函数前添加显式指定符，可以阻止这种隐式转换，从而避免潜在的错误。最后，提到了显式类型转换（Explicitly Typecast）的使用情况。

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1. Conversion Constructor
2. Explicit Specifier
3. Explicitly Typecast

1. Conversion Constructor

#include <iostream> 

using namespace std; 

class Complex 
{ 
private: 
	double real; 
	double imag; 

public: 
	// no default arguments -> a conversion constructor
	Complex(double r = 0.0, double i = 0.0) : real(r), imag(i) {} 

	// A method to compare two Complex numbers 
	bool operator == (Complex rhs) { 
	return (real == rhs.real && imag == rhs.imag)? true : false; 
	} 
}; 

int main() 
{ 
	// a Complex object 
	Complex com1 = {3.0, 0.0}; 

	if (com1 == 3.0) 
	cout << "Same"; 
	else
	cout << "Not Same"; 
	return 0; 
}

Output: Same
Explanation: There are two implicit conversions happened in this code snippet.

Complex com1 = {3.0, 0.0}; Use 2 double numbers to construct a complex object.
if (com1 == 3.0) Use 1 double number to construct a complex object.

2. Explicit Specifier

If we add explicit before Constructor, we then will get an error.

class Complex 
{ 
private: 
	double real; 
	double imag; 

public: 
	// no default arguments -> a conversion constructor
	explicit Complex(double r = 0.0, double i = 0.0) : real(r), imag(i) {} 

	// A method to compare two Complex numbers 
	bool operator == (Complex rhs) { 
	return (real == rhs.real && imag == rhs.imag)? true : false; 
	} 
};

Output: error: chosen constructor is explicit in copy-initialization.

3. Explicitly Typecast

int main() 
{ 
	// a Complex object 
	Complex com1(3.0, 0.0); 

	if (com1 == static_cast<Complex>(3.0)) 
	cout << "Same"; 
	else
	cout << "Not Same"; 
	return 0; 
}