How to Properly Return Error Codes in C Functions Returning Object Pointers

Discover the two best methods to return error codes in C functions that create object pointers without complications. Learn the pros and cons of each approach.
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How to Properly Return Error Codes in C Functions Returning Object Pointers

When developing in C, returning error codes from functions is an important practice, especially when those functions also return object pointers. If you're faced with the challenge of creating an object creation function that needs to signal errors, you may wonder: What is the best way to handle this without complicating the code?

In this article, we'll explore how to return error codes from a function that creates an object pointer, focusing on two main approaches along with their respective advantages. Let's dive in!

The Problem

Suppose you have a function to create an object, defined like this:

[[See Video to Reveal this Text or Code Snippet]]

This function will return a pointer to the object if creation is successful, or 0 if it fails. However, you may need more granularity in error reporting—perhaps ten different error codes to indicate a variety of issues. You might be concerned that mixing the return pointer and error codes is not the best approach. Let's look at how to effectively manage this situation.

Solutions Overview

There are two widely accepted methods for returning error codes from a function that also returns an object pointer:

Return the Object Pointer while Passing Error Result as Parameter:

[[See Video to Reveal this Text or Code Snippet]]

Return the Error Code while Passing a Pointer to the Object:

[[See Video to Reveal this Text or Code Snippet]]

Method 1: Return the Object Pointer while Passing Error Result

In this method, the function returns the pointer directly while you pass an additional parameter to hold the error code. This allows you to write:

[[See Video to Reveal this Text or Code Snippet]]

Pros

Simpler Assignments: The caller can assign the returned object pointer directly.

Less Complexity: This method avoids the need for pointer-to-pointer interfaces.

Method 2: Return the Error Code while Passing a Pointer to the Object

Alternatively, you can design your function to return an error code and modify the object pointer through a parameter. The usage would look like this:

[[See Video to Reveal this Text or Code Snippet]]

Pros

Standard Practice: This method aligns with common industry practices for API design, where functions generally return an error code.

Preserves Original Pointer: If an error occurs, the caller's pointer remains untouched, useful for functions that interface with dynamic memory reallocations.

What to Avoid

While exploring these options, it’s essential to avoid using certain approaches that may complicate your error handling:

Using errno: Relying on a global error code can lead to tricky, error-prone code. It is often not thread-safe and can conflict with error handling from standard libraries.

Wrapper Hacks: Avoid wrapping the returned structure in larger types or allocating memory for error codes at the end of a structure. Such methods increase complexity and the potential for bugs.

Conclusion

In summary, when returning error codes alongside object pointers in C, it is best to choose one of the two outlined methods. They provide clarity and simplicity, improving the maintainability of your code. An effective error handling strategy should be straightforward to avoid introducing new complexities or errors. Remember, an error handler should be simple to ensure better code quality.

Feel free to experiment with both methods and determine which best fits your programming style and project needs. Happy coding!