Question

I think that some newer languages like JS can do this natively, but I forget the term for it (make a “temporary” function in-line just to pass as a callback)

What I want to do is …

I’m writing unit tests where I set up expected input & output messages at compile time. Later at run time, I want to do some checks when each output is received or input has been processed, so I added a parameter for a callback function.

That’s working fine and I could leave it & move on, but … I am just curious …

sometimes a function is overkill and I just need a single comparison; sometime a small block of code would do. Perhaps I could just evaluate these to a zero/non-zero value at run time? But how to pass as a parameter?

At the moment my function has the following signature

void AddExpectedCommand(E_peripheralType peripheral, 
                        communicationBlock_t commandBlock, 
                        errorMessage_t errorMessage, 
                        void *(*DoRunTimeChecks)(E_boolean));

where the final parameter is pointer to a callback function returning boolean.

Is there any way that I could pass a code expression as a parameter instead?

Or does a function seem “cleaner”?

Thanks in advance for any help …

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Update: oops, I got my declaration wrong. I want to pass a pointer so a function which has no parameters and returns an e_Boolean … how do I do that?

Answer 1

With C++11 you can do the following:

Function taking a function that returns a bool:

 void f(function<bool()>);

Call it with a lambda capturing a local variable:

 int x = ...;

 f([&x]() { return (x > 2); });

Or call it with some function g that returns a bool:

bool g();


f(g);

Or bind some function h that takes an int and returns a bool:

bool h(int x);


f(bind(h, 2));  // ie creates a nullary function from h(2)