How do you pass a function as a parameter in C?

Question

I want to create a function that performs a function passed by parameter on a set of data. How do you pass a function as a parameter in C?

Answer 1

This question already has the answer for defining function pointers, however they can get very messy, especially if you are going to be passing them around your application. To avoid this unpleasantness I would recommend that you typedef the function pointer into something more readable. For example.

typedef void (*functiontype)();

Declares a function that returns void and takes no arguments. To create a function pointer to this type you can now do:

void dosomething() { }

functiontype func = &dosomething;
func();

For a function that returns an int and takes a char you would do

typedef int (*functiontype2)(char);

and to use it

int dosomethingwithchar(char a) { return 1; }

functiontype2 func2 = &dosomethingwithchar
int result = func2('a');

There are libraries that can help with turning function pointers into nice readable types. The boost function library is great and is well worth the effort!

boost::function functiontype2;

is so much nicer than the above.