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std::function vs. Function Pointers in C : Which to Choose and When?
When it comes to defining callback functions in C , you have two main options: C-style function pointers and std::function. This choice can significantly impact your code's capabilities and efficiency.
C-Style Function Pointers
Function pointers have been around for a long time and are still widely used. They offer the simplicity of storing a pointer to a function:
void (*callbackFunc)(int);
However, they come with a significant limitation:
Absence of Context Capture: Function pointers cannot retain the context (e.g., captured variables) of the parent function. This means you cannot easily pass lambda functions or call member functions of objects as callbacks.
std::function
std::function (introduced in C 11) was designed to overcome these limitations. It provides a type-safe, generic way to store and pass functions:
std::function< void(int) > callbackFunc;
Advantages of std::function:
Disadvantages of std::function:
Template Parameters
A third option, especially suitable for small functions, is to use a template parameter of a callable object type:
template <typename CallbackFunction> void myFunction(..., CallbackFunction && callback) { ... callback(...); ... }
Advantages of Template Parameters:
Disadvantages of Template Parameters:
Summary Table
To summarize, the following table outlines the key differences between these options:
Feature | Function Pointer | std::function | Template Parameter |
---|---|---|---|
Context Capture | No | Yes | Yes |
Call Overhead | No | Yes | No |
Inlining | No | No | Yes |
Class Member Storage | Yes | Yes | No |
C 11 Support | Yes | No | Yes |
Readability | Less Readable | More Readable | Somewhat Readable |
In most cases, unless you have a specific requirement for function pointers or template parameters, std::function is the preferred choice due to its flexibility, context capture capabilities, and universal compatibility.
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