Question

Let me first explain what I’m trying to achieve using some pseudo-code (JavaScript).

// Declare our function that takes a callback as as an argument, and calls the callback with true.
B(func) { func(true); }

// Call the function
B(function(bool success) { /* code that uses success */ });

I hope this says it all. If not, please comment on my question so I can write a little more to clarify my issue.

What I want is to have code like this in C++.

I have tried to use lambda functions, but I was unable to specify a parameter type for those.

Answer 1

If your compiler is a fairly recent release (such as Visual Studio 2010 or GCC 4.5), you can use some new features from the new C++ standard, which is currently in ratification and should be published soon.

I don’t know what you need to do to enable this in Visual Studio, but it should be well-documented either on MSDN or internal help.

For GCC 4.5, just add the -std=c++0x option to enable the new features.

One of these features is the Lambda syntax:

template <typename F>
void func_with_callback(F f) {
    f(true);
}

int main() {
    func_with_callback( [](bool t){ if(t) cout << "lambda called" << endl; } );
}

If you don’t have access to a modern compiler, you can use techniques such as functors and libraries like boost::lambda, which can perform similarly.