cppLogic errorMedium

Self-assignment in copy assignment operator

Time: 0:00

BugFind the bug and fix the code

What it should do

Assign buffer to itself safely and return stored value. Example: copyBufferValue(42) -> 42

What happens instead

Crash: double free or use-after-free when assigning object to itself

#include <iostream>

class SimpleBuffer {
public:
    int* ptr;
    SimpleBuffer(int v) : ptr(new int(v)) {}
    ~SimpleBuffer() { delete ptr; }
    
    SimpleBuffer& operator=(const SimpleBuffer& other) {
        // Missing self-assignment guard: this == &other deallocates own pointer!
        delete ptr;
        ptr = new int(*other.ptr);
        return *this;
    }
};

int copyBufferValue(int val) {
    SimpleBuffer b(val);
    b = b; // Self assignment deallocates ptr, then dereferences freed memory
    return *b.ptr;
}

int main() {
    std::cout << copyBufferValue(42) << std::endl;
    return 0;
}

Test a custom input to verify an edge case (e.g. empty lists, negative numbers, duplicates).

⏱️0:00

Hints

🏆 0 hints = Flawless Solve

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Hint 2

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Hint 3

Unlocks after Hint 2

This bug belongs to the logic errors pattern

The wrong operator, an inverted condition, a formula the right way round but backwards.

Learn the logic errors pattern Step through your own code

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#include <iostream> class SimpleBuffer { public: int* ptr; SimpleBuffer(int v) : ptr(new int(v)) {} ~SimpleBuffer() { delete ptr; } SimpleBuffer& operator=(const SimpleBuffer& other) { // Missing self-assignment guard: this == &other deallocates own pointer! delete ptr; ptr = new int(*other.ptr); return *this; } }; int copyBufferValue(int val) { SimpleBuffer b(val); b = b; // Self assignment deallocates ptr, then dereferences freed memory return *b.ptr; } int main() { std::cout << copyBufferValue(42) << std::endl; return 0; }

Self-assignment in copy assignment operator

What it should do

What happens instead

More logic errors to practise

Self-assignment in copy assignment operator

What it should do

What happens instead

More logic errors to practise