std::function vs. Function Pointers: When Should You Choose What?

Use std::function, Unless There's a Compelling Reason Not To

When working with callback functions in C , the choice between using a C-style function pointer and the newer std::function can be a matter of debate. Let's examine the pros and cons of each option.

C-Style Function Pointers:

• Advantage: No overhead when calling the function.
• Disadvantage: Cannot capture context variables, limiting their use cases.

std::function:

• Advantage: Can capture context variables, making it more versatile.
• Disadvantage: Introduces a small overhead when calling the function.

When to Use std::function:

In most cases, std::function is the preferred choice. It's more flexible and future-proof than function pointers. Unless there are specific performance concerns, it's generally recommended to use std::function for passing around callbacks.

When to Use Function Pointers:

If performance is a critical consideration and the callback function does not need to capture any context variables, then a function pointer may be a better option. However, this scenario is relatively rare.

Third Option: Template Parameter

Consider using a template parameter if you want the callback function to be any callable object. This approach provides flexibility but requires the outer function to be implemented in the header.

Summary Table:

Feature	Function Pointer	std::function	Template Parameter
Can capture context	No	Yes	Yes
Call overhead	None	Small	None
Can be inlined	No	No	Yes
Can be stored in class member	Yes	Yes	No
Implemented outside of header	Yes	Yes	No
Supported without C 11 standard	Yes	No	Yes
Readability	Poor	Good	Fair

Conclusion:

In general, the advantages of std::function outweigh those of function pointers. It's more flexible, future-proof, and readable. Use function pointers only if there's a specific performance concern or if the callback function does not need to capture any context variables.

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