Defensive Programming

Status Codes

A small status value can explain why a validation step succeeded or failed.

status code Returning a status keeps normal error reporting explicit and traceable.

Status Codes

password
status_codes.cpp
Replay: real traced execution (multi-file project)
#include <iostream>
#include <string>

enum class PasswordStatus {
    ok,
    empty,
    tooShort
};

PasswordStatus checkPassword(const std::string& password) {
    if (password.empty()) {
        return PasswordStatus::empty;
    }
    if (password.size() < 6) {
        return PasswordStatus::tooShort;
    }
    return PasswordStatus::ok;
}

std::string labelFor(PasswordStatus status) {
    if (status == PasswordStatus::ok) {
        return "ok";
    }
    if (status == PasswordStatus::empty) {
        return "empty";
    }
    return "tooShort";
}

int main() {
    std::string password = "safe123";

    PasswordStatus status = checkPassword(password);

    std::cout << "passwordLength=" << password.size() << std::endl;
    std::cout << "status=" << labelFor(status) << std::endl;
    return 0;
}

#include <iostream>
#include <string>

enum class PasswordStatus {
    ok,
    empty,
    tooShort
};

PasswordStatus checkPassword(const std::string& password) {
    if (password.empty()) {
        return PasswordStatus::empty;
    }
    if (password.size() < 6) {
        return PasswordStatus::tooShort;
    }
    return PasswordStatus::ok;
}

std::string labelFor(PasswordStatus status) {
    if (status == PasswordStatus::ok) {
        return "ok";
    }
    if (status == PasswordStatus::empty) {
        return "empty";
    }
    return "tooShort";
}

int main() {
    std::string password = "";

    PasswordStatus status = checkPassword(password);

    std::cout << "passwordLength=" << password.size() << std::endl;
    std::cout << "status=" << labelFor(status) << std::endl;
    return 0;
}

#include <iostream>
#include <string>

enum class PasswordStatus {
    ok,
    empty,
    tooShort
};

PasswordStatus checkPassword(const std::string& password) {
    if (password.empty()) {
        return PasswordStatus::empty;
    }
    if (password.size() < 6) {
        return PasswordStatus::tooShort;
    }
    return PasswordStatus::ok;
}

std::string labelFor(PasswordStatus status) {
    if (status == PasswordStatus::ok) {
        return "ok";
    }
    if (status == PasswordStatus::empty) {
        return "empty";
    }
    return "tooShort";
}

int main() {
    std::string password = "abc";

    PasswordStatus status = checkPassword(password);

    std::cout << "passwordLength=" << password.size() << std::endl;
    std::cout << "status=" << labelFor(status) << std::endl;
    return 0;
}

  1. password ← safe123

    30int main() {31    std::string password→ safe123 = "safe123"; //@password="", "abc"3233    PasswordStatus status = checkPassword(passwordsafe123);

  2. PasswordStatus checkPassword(const std::string& password)

    10PasswordStatus checkPassword(const std::string& passwordsafe123) {11    if (password.empty()) {12        return PasswordStatus::empty;13    }14    if (password.size() < 6) {15        return PasswordStatus::tooShort;16    }17    return PasswordStatus::ok;18}

  3. status ← 0

    33PasswordStatus status→ 0 = checkPassword(passwordsafe123);3435std::cout << "passwordLength=" << passwordsafe123.size() << std::endl;36std::cout << "status=" << labelFor(status0) << std::endl;37return 0;
    outputpasswordLength=7

  4. std::string labelFor(PasswordStatus status)

    20std::string labelFor(PasswordStatus status0) {21    if (status == PasswordStatus::ok) {

  5. if (status == PasswordStatus::ok)

    20std::string labelFor(PasswordStatus status) {21    if (status0 == PasswordStatus::ok) {22        return "ok";23    }

  6. std::cout << "status=" << labelFor(status) << std::endl;

    35    std::cout << "passwordLength=" << password.size() << std::endl;36    std::cout << "status=" << labelFor(status0) << std::endl;37    return 0;38}
    outputstatus=ok

  1. password ← (empty)

    30int main() {31    std::string password→ (empty) = "";3233    PasswordStatus status = checkPassword(password(empty));

  2. PasswordStatus checkPassword(const std::string& password)

    10PasswordStatus checkPassword(const std::string& password(empty)) {11    if (password.empty()) {

  3. if (password.empty())

    10PasswordStatus checkPassword(const std::string& password) {11    if (password(empty).empty()) {12        return PasswordStatus::empty;13    }

  4. status ← 1

    33PasswordStatus status→ 1 = checkPassword(password(empty));3435std::cout << "passwordLength=" << password(empty).size() << std::endl;36std::cout << "status=" << labelFor(status1) << std::endl;37return 0;
    outputpasswordLength=0

  5. std::string labelFor(PasswordStatus status)

    20std::string labelFor(PasswordStatus status1) {21    if (status == PasswordStatus::ok) {

  6. if (status == PasswordStatus::empty)

    23}24if (status1 == PasswordStatus::empty) {25    return "empty";26}

  7. std::cout << "status=" << labelFor(status) << std::endl;

    35    std::cout << "passwordLength=" << password.size() << std::endl;36    std::cout << "status=" << labelFor(status1) << std::endl;37    return 0;38}
    outputstatus=empty

  1. password ← abc

    30int main() {31    std::string password→ abc = "abc";3233    PasswordStatus status = checkPassword(passwordabc);

  2. PasswordStatus checkPassword(const std::string& password)

    10PasswordStatus checkPassword(const std::string& passwordabc) {11    if (password.empty()) {

  3. if (password.size() < 6)

    13}14if (passwordabc.size() < 6) {15    return PasswordStatus::tooShort;16}

  4. status ← 2

    33PasswordStatus status→ 2 = checkPassword(passwordabc);3435std::cout << "passwordLength=" << passwordabc.size() << std::endl;36std::cout << "status=" << labelFor(status2) << std::endl;37return 0;
    outputpasswordLength=3

  5. std::string labelFor(PasswordStatus status)

    20std::string labelFor(PasswordStatus status2) {21    if (status == PasswordStatus::ok) {22        return "ok";23    }24    if (status == PasswordStatus::empty) {25        return "empty";26    }27    return "tooShort";28}

  6. std::cout << "status=" << labelFor(status) << std::endl;

    35    std::cout << "passwordLength=" << password.size() << std::endl;36    std::cout << "status=" << labelFor(status2) << std::endl;37    return 0;38}
    outputstatus=tooShort