blocks|key|384369|text|在这种情况下，你最好跳过对自我赋值的检查--当你只赋值一个似乎是简单类型(可能是双精度类型)的成员时，通常比避免赋值更快，所以你最终会得到：|type|unstyled|depth|inlineStyleRanges|entityRanges|data|384370|SimpleCircle+&+SimpleCircle::operator=(const+SimpleCircle+&+rhs)
{
++++itsRadius+=+rhs.getRadius();+//+or+just+`itsRadius+=+rhs.itsRadius;`
++++return+*this;
}|code-block|syntax|javascript|384371|我意识到许多旧的和/或质量较低的书建议检查自我分配。然而，至少在我的经验中，没有它你会过得更好的情况非常罕见(如果操作员依赖于它的正确性，它几乎肯定不是异常安全的)。|384372|顺便说一句，为了定义一个圆，你通常需要一个圆心和一个半径，当你复制或赋值时，你想要同时复制/赋值。|384373|entityMap^0|0|0|0|0^^$0|@$1|2|3|4|5|6|7|M|8|@]|9|@]|A|$]]|$1|B|3|C|5|D|7|N|8|@]|9|@]|A|$E|F]]|$1|G|3|H|5|6|7|O|8|@]|9|@]|A|$]]|$1|I|3|J|5|6|7|P|8|@]|9|@]|A|$]]|$1|K|3|-4|5|6|7|Q|8|@]|9|@]|A|$]]]|L|$]]

Under the circumstances, you're almost certainly better off skipping the check for self-assignment -- when you're only assigning one member that seems to be a simple type (probably a double), it's generally faster to do that assignment than avoid it, so you'd end up with:

<pre><code>SimpleCircle &amp; SimpleCircle::operator=(const SimpleCircle &amp; rhs)
{
 itsRadius = rhs.getRadius(); // or just `itsRadius = rhs.itsRadius;`
 return *this;
}
</code></pre>

I realize that many older and/or lower quality books advise checking for self assignment. At least in my experience, however, it's sufficiently rare that you're better off without it (and if the operator depends on it for correctness, it's almost certainly not exception safe).

As an aside, I'd note that to define a circle, you generally need a center and a radius, and when you copy or assign, you want to copy/assign both.

blocks|key|600318|text|这是使用操作符重载的正确方法，现在你可以通过引用来获取对象，避免了值复制。|type|unstyled|depth|inlineStyleRanges|entityRanges|data|600319|entityMap^0|0^^$0|@$1|2|3|4|5|6|7|D|8|@]|9|@]|A|$]]|$1|B|3|-4|5|6|7|E|8|@]|9|@]|A|$]]]|C|$]]

it's right way to use operator overloading
now you get your object by reference
avoiding value copying.

blocks|key|384504|text|这可能会有所帮助：|type|unstyled|depth|inlineStyleRanges|entityRanges|data|384505|//+Operator+overloading+in+C%2B%2B
//assignment+operator+overloading
#include<iostream>
using+namespace+std;

class+Employee
{
private:
int+idNum;
double+salary;
public:
Employee+(+)+{
++++idNum+=+0,+salary+=+0.0;
}

void+setValues+(int+a,+int+b);
void+operator=+(Employee+&emp+);

};

void+Employee::setValues+(+int+idN+,+int+sal+)
{

salary+=+sal;+idNum+=+idN;

}

void+Employee::operator+=+(Employee+&emp)++//+Assignment+operator+overloading+function
{
salary+=+emp.salary;
}

int+main+(+)
{

Employee+emp1;
emp1.setValues(10,33);
Employee+emp2;
emp2+=+emp1;+//+emp2+is+calling+object+using+assignment+operator

}|code-block|syntax|javascript|384506|entityMap^0|0|0^^$0|@$1|2|3|4|5|6|7|I|8|@]|9|@]|A|$]]|$1|B|3|C|5|D|7|J|8|@]|9|@]|A|$E|F]]|$1|G|3|-4|5|6|7|K|8|@]|9|@]|A|$]]]|H|$]]

this might be helpful:

<pre><code>// Operator overloading in C++
//assignment operator overloading
#include&lt;iostream&gt;
using namespace std;

class Employee
{
private:
int idNum;
double salary;
public:
Employee ( ) {
 idNum = 0, salary = 0.0;
}

void setValues (int a, int b);
void operator= (Employee &amp;emp );

};

void Employee::setValues ( int idN , int sal )
{

salary = sal; idNum = idN;

}

void Employee::operator = (Employee &amp;emp) // Assignment operator overloading function
{
salary = emp.salary;
}

int main ( )
{

Employee emp1;
emp1.setValues(10,33);
Employee emp2;
emp2 = emp1; // emp2 is calling object using assignment operator

}
</code></pre>

blocks|key|384519|text|#include<iostream>

using+namespace+std;

class+employee
{
++++int+idnum;
++++double+salary;
++++public:
++++++++employee(){}

++++++++employee(int+a,int+b)
++++++++{
++++++++++++idnum=a;
++++++++++++salary=b;
++++++++}

++++++++void+dis()
++++++++{
++++++++++++cout<<"1st+emp:"<<endl<<"idnum="<<idnum<<endl<<"salary="<<salary<<endl<<endl;
++++++++}

++++++++void+operator=(employee+&emp)
++++++++{
++++++++++++idnum=emp.idnum;
++++++++++++salary=emp.salary;
++++++++}

++++++++void+show()
++++++++{
++++++++++++cout<<"2nd+emp:"<<endl<<"idnum="<<idnum<<endl<<"salary="<<salary<<endl;
++++++++}
};

main()
{
++++int+a;
++++double+b;

++++cout<<"enter+id+num+and+salary"<<endl;
++++cin>>a>>b;
++++employee+e1(a,b);
++++e1.dis();
++++employee+e2;
++++e2=e1;
++++e2.show();++
}|type|code-block|depth|inlineStyleRanges|entityRanges|data|syntax|javascript|384520|unstyled|entityMap^0|0^^$0|@$1|2|3|4|5|6|7|G|8|@]|9|@]|A|$B|C]]|$1|D|3|-4|5|E|7|H|8|@]|9|@]|A|$]]]|F|$]]

<pre><code>#include&lt;iostream&gt;

using namespace std;

class employee
{
 int idnum;
 double salary;
 public:
 employee(){}

 employee(int a,int b)
 {
 idnum=a;
 salary=b;
 }

 void dis()
 {
 cout&lt;&lt;"1st emp:"&lt;&lt;endl&lt;&lt;"idnum="&lt;&lt;idnum&lt;&lt;endl&lt;&lt;"salary="&lt;&lt;salary&lt;&lt;endl&lt;&lt;endl;
 }

 void operator=(employee &amp;emp)
 {
 idnum=emp.idnum;
 salary=emp.salary;
 }

 void show()
 {
 cout&lt;&lt;"2nd emp:"&lt;&lt;endl&lt;&lt;"idnum="&lt;&lt;idnum&lt;&lt;endl&lt;&lt;"salary="&lt;&lt;salary&lt;&lt;endl;
 }
};

main()
{
 int a;
 double b;

 cout&lt;&lt;"enter id num and salary"&lt;&lt;endl;
 cin&gt;&gt;a&gt;&gt;b;
 employee e1(a,b);
 e1.dis();
 employee e2;
 e2=e1;
 e2.show(); 
}
</code></pre>

I have used the following code for assignment operator overloading:

<pre><code>SimpleCircle SimpleCircle::operator=(const SimpleCircle &amp; rhs)
{
 if(this == &amp;rhs)
 return *this;
 itsRadius = rhs.getRadius();
 return *this;
}
</code></pre>

My Copy Constructor is this:

<pre><code>SimpleCircle::SimpleCircle(const SimpleCircle &amp; rhs)
{
 itsRadius = rhs.getRadius();
}
</code></pre>

In the above operator overloading code, copy constructor is called as there is a new object is being created; hence I used the below code:

<pre><code>SimpleCircle &amp; SimpleCircle::operator=(const SimpleCircle &amp; rhs)
{
 if(this == &amp;rhs)
 return *this;
 itsRadius = rhs.getRadius();
 return *this;
}
</code></pre>

Its working perfectly and the copy constructor problem is avoided, but is there any unknown issues (to me) regarding this ?

assignment operator overloading in c++

我使用了以下代码来实现赋值运算符重载：SimpleCircle SimpleCircle::operator=(const SimpleCircle & rhs){     if(this == &rhs)        return *this;     itsRadius = rhs.getRadius();   ...

问c++中的赋值运算符重载
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