JuniorTheoryVery common

What happens when this program runs?

C++

#include <iostream>

int* positive(int* p) {
    return *p > 0 ? p : nullptr;
}

int main() {
    int x = -7;
    std::cout << *positive(&x) << '\n';
}

Undefined behavior: positive returns nullptr, and * dereferences it

Expecting a guaranteed crash: dereferencing nullptr is undefined behavior, and the standard promises no crash or any other outcome.
Expecting a compile error: the compiler does not check which pointer may be nullptr, so the program builds without an error.

How would you change main so that it prints x only when positive does not return nullptr?
Why would a reference be a poor return type for positive?

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Back to questions

JuniorTheoryVery common

What happens when this program runs?

C++

#include <iostream>

int* positive(int* p) {
    return *p > 0 ? p : nullptr;
}

int main() {
    int x = -7;
    std::cout << *positive(&x) << '\n';
}

Undefined behavior: positive returns nullptr, and * dereferences it

Expecting a guaranteed crash: dereferencing nullptr is undefined behavior, and the standard promises no crash or any other outcome.
Expecting a compile error: the compiler does not check which pointer may be nullptr, so the program builds without an error.

How would you change main so that it prints x only when positive does not return nullptr?
Why would a reference be a poor return type for positive?

Back to questions Open topic in roadmap →Answer it yourself — Quiz