Null Pointer

nullptr means a pointer is not pointing at an object.

null_pointer.cpp

#include <iostream>

int main() {
    bool hasValue = ;
    int value = ;
    int fallback = -1;
    int* maybeValue = nullptr;

    if (hasValue) {
        maybeValue = &value;
    }

    int result = fallback;
    if (maybeValue != nullptr) {
        result = *maybeValue;
    }

    std::cout << "hasValue=" << hasValue << std::endl;
    std::cout << "result=" << result << std::endl;
    return 0;
}

#include <iostream>

int main() {
    bool hasValue = ;
    int value = ;
    int fallback = -1;
    int* maybeValue = nullptr;

    if (hasValue) {
        maybeValue = &value;
    }

    int result = fallback;
    if (maybeValue != nullptr) {
        result = *maybeValue;
    }

    std::cout << "hasValue=" << hasValue << std::endl;
    std::cout << "result=" << result << std::endl;
    return 0;
}

#include <iostream>

int main() {
    bool hasValue = ;
    int value = ;
    int fallback = -1;
    int* maybeValue = nullptr;

    if (hasValue) {
        maybeValue = &value;
    }

    int result = fallback;
    if (maybeValue != nullptr) {
        result = *maybeValue;
    }

    std::cout << "hasValue=" << hasValue << std::endl;
    std::cout << "result=" << result << std::endl;
    return 0;
}

#include <iostream>

int main() {
    bool hasValue = ;
    int value = ;
    int fallback = -1;
    int* maybeValue = nullptr;

    if (hasValue) {
        maybeValue = &value;
    }

    int result = fallback;
    if (maybeValue != nullptr) {
        result = *maybeValue;
    }

    std::cout << "hasValue=" << hasValue << std::endl;
    std::cout << "result=" << result << std::endl;
    return 0;
}

#include <iostream>

int main() {
    bool hasValue = ;
    int value = ;
    int fallback = -1;
    int* maybeValue = nullptr;

    if (hasValue) {
        maybeValue = &value;
    }

    int result = fallback;
    if (maybeValue != nullptr) {
        result = *maybeValue;
    }

    std::cout << "hasValue=" << hasValue << std::endl;
    std::cout << "result=" << result << std::endl;
    return 0;
}

#include <iostream>

int main() {
    bool hasValue = ;
    int value = ;
    int fallback = -1;
    int* maybeValue = nullptr;

    if (hasValue) {
        maybeValue = &value;
    }

    int result = fallback;
    if (maybeValue != nullptr) {
        result = *maybeValue;
    }

    std::cout << "hasValue=" << hasValue << std::endl;
    std::cout << "result=" << result << std::endl;
    return 0;
}

nullptr Check a pointer before dereferencing when it might be `nullptr`.