Double free or corruption (fasttop) error when trying to use setter

Question

I have created a basic class object with setter and getters based on the text book. The code work fine but when I attempt to change the data in name from Square to Circle, I get error : double free or corruption (fasttop).

Can someone enlighten me what is happening here? Is this due to some kind of memory allocation error?

Below is a reproducible code:

#include <iostream>
#include <string>
#include <cstring>

using namespace std;

class Shape
{
    protected:
        string name;
        bool contains = false;
        
    public:
        Shape(string name, bool contains)
        {
            setName(name);
            setContains(contains);
        }
        
        string getName();
        bool getContains();
        string setName(string name);
        bool setContains(bool contains);
};

string Shape :: setName(string inputName)
{
    name = inputName;
}

bool Shape :: setContains(bool inputContains)
{
    contains = inputContains;
}

string Shape :: getName()
{
    return name;
}

bool Shape :: getContains()
{
    return contains;
}

int main()
{
    Shape object1("Square", true);
    cout << "Testing" << endl;
    cout << object1.getName() << endl;
    cout << object1.getContains() << endl;

    object1.setName("Circle");
    cout << object1.getName() << endl;
    return 0;
}

Edit:

Interesting, when running the code in OnlineGDB without object1.setName("Circle"); and cout << object1.getName() << endl; will report a segmentation fault error. What is the way to tackle this issue?

Your setName and setContains function promise to return something but don't. This is undefined behavior. Isn't your compiler throwing warnings about these lines? — Botje, Jul 28 '20 at 11:38
When I compile it, it didn't say any error. I am using Ubuntu terminal to do this. — user3118602, Jul 28 '20 at 11:38
Sorry, may I know the purpose of the command? As this is a virtual environment provided by the school, they specifically told us not to mess around with any of the setup in the Ubuntu. — user3118602, Jul 28 '20 at 11:41
If I run this in onlinegdb, the same error appear too if that helps anyone to explain to me what is going on. — user3118602, Jul 28 '20 at 11:42
You can use valgrind to better analyze and identify the cause of this issue. — buchipper, Jul 28 '20 at 11:43
The root cause is still the same: you promised to return something and did not, the program is crashing as a result. Those flags tell the compiler to check your code for common programming errors and tell you about them. Add them to the the line where you call `g++` or `clang++`. — Botje, Jul 28 '20 at 11:48

score 0 · Accepted Answer · answered Jul 28 '20 at 12:15

0

Your setName and setContains functions don't have any return statements while their return types are not void. Therefore, executing these functions invokes undefined behavior.

N3337 6.6.3 The return statement says:

Flowing off the end of a function is equivalent to a return with no value; this results in undefined behavior in a value-returning function.

To fix this issue, you should do one of:

Change return types of the functions setName and setContains to void.
Add return statements with proper return value to the functions.

answered Jul 28 '20 at 12:15

MikeCAT

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Hi Mike. Thank you, I don't really understand the second point. When you mentioned to add `return` statement with proper return value to functions, do you mean to say that I need to put the datatype in setName for the `name` and `contains` variables? – user3118602 Jul 28 '20 at 13:19
No. The variables `name` and `coutains` already have the datatype in the class declaration, so you don't need to give them the datatype again. – MikeCAT Jul 28 '20 at 13:21
Thanks Mike, took me awhile but I finally understood! – user3118602 Jul 28 '20 at 13:25

Double free or corruption (fasttop) error when trying to use setter

1 Answers1