cppScope errorMedium

Lambda capturing local reference outlives stack frame

Time: 0:00

BugFind the bug and fix the code

What it should do

Create multiplier function and evaluate on value. Example: generateMultiplierLambda(3, 4) -> 12

What happens instead

Segmentation fault or garbage multiplication result due to dangling reference capture

#include <iostream>
#include <functional>

std::function<int(int)> makeMultiplier(int factor) {
    // Capturing factor by reference [&] captures local stack variable
    return [&](int x) { return x * factor; };
}

int generateMultiplierLambda(int factor, int val) {
    auto fn = makeMultiplier(factor);
    return fn(val);
}

int main() {
    std::cout << generateMultiplierLambda(3, 4) << std::endl;
    return 0;
}

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

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This bug belongs to the scope and closure bugs pattern

Every callback reports the last value, a counter never increments, UnboundLocalError on a variable you can see.

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#include <iostream> #include <functional> std::function<int(int)> makeMultiplier(int factor) { // Capturing factor by reference [&] captures local stack variable return [&](int x) { return x * factor; }; } int generateMultiplierLambda(int factor, int val) { auto fn = makeMultiplier(factor); return fn(val); } int main() { std::cout << generateMultiplierLambda(3, 4) << std::endl; return 0; }

Lambda capturing local reference outlives stack frame

What it should do

What happens instead

More scope and closure bugs to practise

Lambda capturing local reference outlives stack frame

What it should do

What happens instead

More scope and closure bugs to practise