Handling self-assignment problems in assignment operators

Self-assignment occurs when an object is assigned to itself, for example:

val = val;

Vec[i] = vec[j];//potential self-assignment (I=J)

*p = *q; potential self-assignment

Class A

{

a& operator= (const a& RHS)//unsafe assignment version

{

Delete p;//stop using the current object

p = new P (RHS.P);//Use copy of RHS

return *this;

}

B p;

}

Solution One: The use of certificates and testing

a& operator= (const a& RHS)

{

if (this = = &RHS) return *this; Certificate and test

Delete p;//stop using the current object

p = new B (RHS.P);//Use copy of RHS

return *this;

}

This version has an exception security, if new has an exception or B uses copy to construct the exception, a will eventually hold a pointer to a deleted b

Solution Two: Remember the original object

a& operator= (const a& RHS)

{

B *pp = p;//Remember the original p

p = new B (RHS.P);//Another P points to a copy of the *p

Delete pp;//Remove the original p

return *this;

}

Handling self-assignment problems in assignment operators