调用重载赋值 function 时向量未正确重新初始化

Question

I have a class "SecretMessages" that utilizes operator overloading with both copy and assign. It has 3 data members, most importantly a vector messages, and a vector message_views which corresponds to the number of remaining views of each message. The issue I'm having is when the assignment operator is called the vectors are not being reinitialized properly. So even though I'm able to read all of the data being copied over just fine inside of the function, when it is called on an L value these values do not update the vector.

My class definition looks as such:

class SelfDestructingMessage {
     public:
         vector<string> messages;
         long number_of_allowed_views;
         vector<long> message_views; // keeps track of each message view 
         ... 
         SelfDestructingMessage(SelfDestructingMessage &sdm); // copy 
         SelfDestructingMessage operator = (SelfDestructingMessage &sdm); // assign };

And here is the output from the test file I have been running, which creates a new SecretMessage object and assigns it to one that has been previously defined.

sdm4:       //message_views print is empty before assignment
ASSIGNMENT OP
printing out message_views after assign:
0
2
1
END ASSIGNMENT
sdm4 after message views after assignment: 
0
0
0

I'm not sure why the message_views vector of sdm4 isn't updating after *this is returned even though the values 0, 1, and 2 are all in the messages vector in assignment function. Any ideas?

Answer 1

Looks like the return from your assignment is copying the object, so your return statement calls your copy constructor. You didn't send us that, but if it clears its argument, it's clearing *this.

Try changing the return type of the assignment operator to SelfDestructingMessage &, so that copy is not invoked.