Error handling is an important aspect of software development. It allows developers to handle unexpected or erroneous situations in a program. In legacy C++ code, error handling was often done using error codes or throwing and catching exceptions. However, modern C++ provides several improvements in error handling techniques that make code more robust and efficient. In this article, we will explore some of these improvements.

Table of Contents

• Introduction
• Exception Handling
• RAII (Resource Acquisition Is Initialization)
• std::expected
• Conclusion

Introduction

In legacy C++ code, the most common error handling mechanism was to return error codes from functions. However, this approach had several downsides. It required developers to manually check and propagate error codes, which could lead to cumbersome and error-prone code. Additionally, it made it difficult to write a clean and concise code that separates error handling from normal program flow.

Exception Handling

In modern C++, the most widely-used error handling mechanism is exception handling. Exceptions allow developers to throw an exception when an error or exceptional condition occurs, and catch it at an appropriate location in the code to handle the error gracefully. This provides a clear separation between normal code execution and error handling.

try {
    // Code that may throw an exception
    throw MyException("Something went wrong!");
} catch(const MyException& ex) {
    // Handle the exception
    std::cout << "Caught exception: " << ex.what() << std::endl;
}

With exception handling, you can propagate the error up the call stack without having to manually pass error codes. It also allows you to catch and handle exceptions at different levels of the code, providing flexibility and modularity.

RAII (Resource Acquisition Is Initialization)

Another improvement in error handling in modern C++ comes from the RAII (Resource Acquisition Is Initialization) idiom. RAII is a technique that ties the lifetime of a resource (like memory allocation or file handle) to the lifetime of an object. When the object goes out of scope, its destructor is automatically called, ensuring that the resource is properly cleaned up.

This automatic resource cleanup mechanism is particularly useful for handling errors. If an error occurs during the execution of a function, the destructors of local objects will be called, ensuring that any allocated resources are properly released.

class FileHandle {
public:
    FileHandle(const std::string& filename) {
        // Open the file
    }
    
    ~FileHandle() {
        // Close the file
    }
    
    // ...
};

void doSomethingWithFile() {
    FileHandle file("data.txt");
    // Code that may throw an exception
    throw MyException("Something went wrong!");
}

int main() {
    try {
        doSomethingWithFile();
    } catch(const MyException& ex) {
        // Handle the exception
        std::cout << "Caught exception: " << ex.what() << std::endl;
    }
}

By using RAII, you can ensure that resources are properly released, even in the presence of exceptions. This improves both the reliability and readability of code.

std::expected

In addition to exception handling, modern C++ introduces the std::expected type for error handling. std::expected is a type that represents the expected result of an operation, which can either hold a value or an error. This provides a more explicit way of handling errors, as it forces the developer to explicitly check whether an operation was successful or resulted in an error.

std::expected<int, std::string> divide(int x, int y) {
    if (y == 0) {
        return std::make_unexpected("Division by zero");
    }
    
    return x / y;
}

void doSomething() {
    auto result = divide(10, 0);
    
    if (result) {
        std::cout << "Result: " << *result << std::endl;
    } else {
        std::cout << "Error: " << result.error() << std::endl;
    }
}

std::expected provides a clear interface for error handling and eliminates the need for using exceptions in some cases. It can be particularly useful in scenarios where exceptions are expensive, such as in low-latency applications or resource-constrained environments.

Conclusion

Modern C++ provides several improvements in error handling compared to legacy code. Exception handling allows for cleaner and more modular code, while RAII ensures proper resource cleanup even in the presence of exceptions. Additionally, the introduction of std::expected provides a more explicit and efficient way of handling errors. By leveraging these techniques, developers can write more robust and maintainable code.

#cpp #errorhandling