Assignment operator overloading in C type problem return values and parameters-CodePudding

description : for custom types, the assignment operator overloading in the code below I function return values and parameters of type why must be a reference type (if it is not a reference type, the program will go wrong, errors in the code below)? annotation part is my own understanding , the great god please help see what mistake help me correct the, first thank you,

 
# include 
using namespace std; 

//the assignment operator overloading 
The class Person 
{
Public: 
The Person (int age) 
{
M_Age=new int (age); 

} 

//parameter must be a reference type, and if the value type, at the end of the function performed when the destructor the pointer (incoming p. _Age) to release the memory space. 
Person& Operator=(Person & amp; P) 
{

//if you have not release the heap area space, first release 
If (m_Age!=NULL) 
{
The delete m_Age; 
M_Age=NULL; 
} 

M_Age=new int (* p. _Age); 
return *this; 
} 

To the Person (s) 
{
If (m_Age!=NULL) 
{
The delete m_Age; 
M_Age=NULL; 
} 
} 

Int * m_Age; 
}; 

Void test01 () 
{
The Person p1 (18); 
The Person p2 (20); 
The Person p3 (30); 

P3=p2=p; 

//for a custom data types, the equality operator overloading return value must be a reference type 
//such as the above code is equivalent to p3. Operator=(p2) operator=(p1)); , including process parameter passing 
That Person & amp; P=p2. Operator=(p1); , if the operator=() function returns the value type 
//will first create a temporary object in memory temp is used to transfer to receive a copy of the object, and then use the temporary object initialization for reference p 
//and temporary object life cycle is very short, only at the end of the current statement released its memory space, then accessed through p temp memory space is illegal operation, 

Cout & lt; <"The age of the p1 for:" & lt; <* p1 m_Age & lt; 
Cout & lt; <"Age of p2:" & lt; <* the p2 m_Age & lt; 
Cout & lt; <"Age of p3:" & lt; <* p3 m_Age & lt; } 

Int main (void) 
{
Test01 (); 
system("pause"); 
return 0; 
}

error:

Case1: when the return value is not a reference type hint:

Binary "=" error C2679: found no accept "Person" type of the right operand operator (or no acceptable conversion)

Case2: when the parameter is not a reference type hint:

CodePudding user response:

The return value is allowed, you wrong, because you aren't judging self assignment
Is T a;
A=a;//this form

When this form when
Your operator=
Put a age deleted in assigned to a, so wrong,
The return value, its defect is more than a copy, inefficient

CodePudding user response:

And your class does not define the copy constructor,
The Person & amp; P=p2. Operator=(p1);
By default copy constructor, the compiler will automatically provide, it is the implementation of the target and the original object binary assignment,
P this sentence has been completed and p2 age point to the same memory region, so that when an object after the release, the next object release will go wrong again,

CodePudding user response:

reference 1/f, the truth is right or wrong response:

the return value is allowed, you assignment error because you don't judge yourself
Is T a;
A=a;//this form

I added the assignment after the judgment of the self or hint:
Binary "=" error C2679: found no accept "Person" type of the right operand operator (or no acceptable conversion)

 
# include 
using namespace std; 

//the assignment operator overloading 
The class Person 
{
Public: 
The Person (int age) 
{
M_Age=new int (age); 
} 

//overloaded assignment operator, with deep copy to solve the problem of shallow copy 
//create a new space will be copied on heap area object pointer members is pointing to the value of the copied "
//parameter must be a reference type, and if the value type, at the end of the function performed when the destructor the pointer (incoming p. _Age) to release the memory space. 
The Person operator=(Person & amp; P) 
{
//determine whether self assignment 
If (& amp; P==this) 
{
return *this; 
} 

//if you have not release the heap area space, first release 
If (m_Age!=NULL) 
{
The delete m_Age; 
M_Age=NULL; 
} 

//deep copy 
M_Age=new int (* p. _Age); 
return *this; 
} 

To the Person (s) 
{
If (m_Age!=NULL) 
{
The delete m_Age; 
M_Age=NULL; 
} 
} 

Int * m_Age; 
}; 

Void test01 () 
{
The Person p1 (18); 
The Person p2 (20); 
The Person p3 (30); 

P3=p2=p; 


//such as the above code is equivalent to p3. Operator=(p2) operator=(p1)); Process, in which parameters namely Person & amp; P=p2. Operator=(p1); If the operator=() function returns the value 
//will first create a temporary object in memory temp is used to transfer to receive a copy of the object, and then use the temporary object initialization for reference p 
//and temporary object statement cycle is very short, only at the end of the current statement released its memory space, then accessed through p temp memory space is illegal operation, 



Cout & lt; <"The age of the p1 for:" & lt; <* p1 m_Age & lt; 
Cout & lt; <"Age of p2:" & lt; <* the p2 m_Age & lt; 
Cout & lt; <"Age of p3:" & lt; <* p3 m_Age & lt; } 


Int main (void) 
{
Test01 (); 
system("pause"); 
return 0; 
}

CodePudding user response:

The Person operator=( const Person & amp; p)