Summary - Advanced error handling
- C++ course
- Advanced
- Lesson 78/83
- 5 min
Combine exception safety, RAII and std::expected to write a safe class.
Summary - Advanced error handling
In this group you learned exception hierarchy, exception safety, RAII, std::expected and noexcept.
Exceptions are organised in the std::exception hierarchy; safety guarantees (basic, strong, nothrow) are the basis of robust code; RAII ties resources to objects; std::expected returns errors as values; the noexcept contract gives a no-throw guarantee. Now you will write a SafeStack class that combines these ideas: it will manage data with RAII, return std::expected from pop, and mark empty as noexcept.
Practice Write a SafeStack class
Write a SafeStack class: it has a std::vector<int> data_ member; void push(int v) adds; std::expected<int, std::string> pop() returns std::unexpected(std::string("empty stack")) when empty, otherwise the value; bool empty() const noexcept returns data_.empty(). In main call s.push(42), auto r = s.pop() and if r.has_value() print r.value().
Starter code
#include <iostream>
#include <vector>
#include <expected>
#include <string>
// Write the SafeStack class: push, pop (expected), empty (noexcept)
int main() {
// Create a stack, add a value, pop it and print
return 0;
}Sample solution
#include <iostream>
#include <vector>
#include <expected>
#include <string>
class SafeStack {
std::vector<int> data_;
public:
void push(int v) { data_.push_back(v); }
std::expected<int, std::string> pop() {
if (data_.empty()) return std::unexpected(std::string("empty stack"));
int v = data_.back();
data_.pop_back();
return v;
}
bool empty() const noexcept { return data_.empty(); }
};
int main() {
SafeStack s;
s.push(42);
auto r = s.pop();
if (r.has_value()) std::cout << r.value();
return 0;
}Expected output
42
Questions and answers
Review the lesson questions together with their answers. To test yourself, solve the lesson interactively.
1 the SafeStack pop call
auto r = s.____();auto r = s.pop();Explanation: s.pop() returns std::expected.
2 Match each idea to its description
| Term | Meaning |
|---|---|
hierarchy |
Exception tree |
safety |
Guarantee level |
RAII |
Resource tied to object |
expected |
Error as value |
3 Which idea returns errors as values instead of exceptions?
- RAII
- std::expected Correct answer
- noexcept
- hierarchy
Explanation: std::expected gives the error as a return value.