Return Error Values vs. Exceptions in C++

#Mastering Error Handling in C++: When to Use What

#Return Values: Handling Expected Failures

Return values are best suited for situations where a failure is an expected or reasonably common outcome of a function's operation. The caller is anticipated to check the return value and react accordingly.

#Key Scenarios for Return Values

• Anticipated Failures as Part of Normal Operation: Think of a function that tries to find an item in a list. If the item isn't there, that's not a catastrophic error; it's just a common search result.
• Example: A parseConfigFile() function might return a bool to indicate true for success and false if the file format was invalid. The calling code expects to handle both outcomes.
• Performance-Critical Code: In highly optimized loops or low-latency systems, the overhead associated with throwing and catching exceptions can be a performance bottleneck. Returning values is generally much faster when failures are frequent.
• Low-Level APIs & C Compatibility: When designing libraries or modules that need to interface with C or other languages that don't support exceptions, return codes are the standard.
• Simple Success/Failure Indication: For operations where a binary success/failure is sufficient, a bool or an integer error code works perfectly.

#Modern C++ Tools for Return Values

• std::optional<T> (C++17) This is ideal when a function might successfully compute a value, or it might compute nothing. It represents the potential absence of a value.
  • Example: A findUserById(int id) function could return std::optional<User>: if the user exists, you get the User object; otherwise, an empty std::optional indicates the user wasn't found. This clearly communicates that a value might not be present, rather than using a special "null" value or an error code.
• std::expected\<T, E\> (C++23): This is a powerful new tool for fallible operations. A function returns an std::expected object, which either holds a successful value of type T or an error value of type E.
  • Example: A connectToServer(const std::string& address) function might return std::expected<Connection, ConnectionError>. You explicitly check if it holds a Connection or a ConnectionError (which could detail network issues, authentication failures, etc.). This forces explicit handling of both success and specific error paths, improving clarity and safety.

#Exceptions: Managing Exceptional Circumstances

Exceptions are designed for truly exceptional conditions – situations that represent a deviation from the normal execution flow, something that "shouldn't happen" in a well-behaved program, or a violation of a function's contract (its promised behavior).

#Key Scenarios for Exceptions

• Truly Exceptional Errors: These are problems that prevent a function from fulfilling its purpose. If a critical resource is unavailable or an operation is fundamentally impossible given the inputs.
  • Examples: std::bad_alloc (out of memory), std::out_of_range (accessing an array beyond its bounds), or failure to open a critical configuration file without which the program cannot function.
• Error Propagation Through Multiple Layers: When an error occurs deep within a nested function call stack, and the appropriate place to handle it is much higher up. Exceptions automatically "unwind" the stack, destroying objects in scope (thanks to RAII - Resource Acquisition Is Initialization) until a catch block is found. This avoids tedious manual error code propagation.
• Constructors: Constructors cannot return values, so throwing an exception is the only way to signal that object creation failed. (Note: Destructors should generally not throw exceptions, as it can lead to std::terminate if another exception is already active).
• Rich Error Information: Exceptions are objects themselves, allowing you to encapsulate detailed information about the error (e.g., error messages, specific error codes, contextual data, or even a stack trace). This makes debugging and logging much more informative.
• Enforcing Error Handling: An unhandled exception will typically terminate the program. This forces developers to acknowledge and handle critical error conditions, preventing the program from continuing in an invalid or undefined state.

#Comparative Summary

#Best Practices for Robust C++ Error Handling

• The "Expected vs. Exceptional" Rule: Use return values for anticipated failures; use exceptions for truly abnormal situations.
• Embrace RAII: Always use RAII for resource management to ensure exception safety.
• Avoid exceptions for control flow: Do not use exceptions for regular branching logic.
• Prefer std::expected for fallible operations: It provides clear, type-safe handling for functions that may fail.
• Consistency is key: Establish and follow a consistent error-handling strategy within your team or project.