How to Correctly Pass Class Member Functions as Callbacks in C ?

Overcoming Compilation Errors when Passing Class Member Functions as Callbacks

You encounter compilation errors when passing a class member function as a callback due to misunderstandings about the syntax and the hidden "this" parameter in member functions.

Clarifying Member Functions

Member functions are not standalone functions but rather functions with an additional hidden "this" pointer. This pointer references the instance of the class that the function belongs to. When calling a member function using class instance syntax (e.g., object.memberFunction()), the compiler automatically determines the value of "this."

Syntax conundrum

Your initial approach failed because you attempted to pass &CLoggersInfra::RedundencyManagerCallBack as a callback. This function pointer lacks the necessary "this" pointer. The correct syntax is:

m_cRedundencyManager->Init(std::bind(&CLoggersInfra::RedundencyManagerCallBack, this));

Unveiling the Hidden "this"

You want to pass a callback that specific to a particular instance of the CLoggersInfra class. To account for the hidden "this" pointer, you need to bind it explicitly.

std::bind1st and boost::bind Rescue

Use std::bind1st or boost::bind to bind the "this" pointer, creating a new function that takes the instance as a hidden parameter and the callback's original parameters as usual. This resolves the compilation issue.

The Hidden Catch

Init requires a raw function pointer, which boost::bind does not provide out of the box. However, StackOverflow offers a solution to convert boost::functions to raw pointers.

C 11 Update with Lambda Functions

In C 11 and later, lambda functions that capture "this" can replace boost::bind for this purpose.

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