Pointer to function with some, but not all arguments fixed

Question

I want to use Brents method as present in the Numerical Recepies Book to minimize a function. The signature of the minimzation routine essentially looks like this:

float brent(float (*f)(float), float *xmin, "other parameters not relevant to question")

As you can guess brent returns the minimum value of f and stores its argument in xmin. However, the exact form of the function I want to minimize depends on additional parameters. Say

float minimize_me(float x, float a, float b)

Once I decided on the values of a and b I want to minimize it with respect to x.

I could simply add additional arguments to all functions called, all the way down to brent, thus changing its signature to

float brent(float (*f)(float,float,float),float a ,float b , float *xmin, ...)

and consequently call (*f)(x,a,b) inside brent every time. This, however, seems not really elegant to me since I would now have to pass not only the pointer to minimize_me, but also two additional parameters down a whole chain of functions.

I suspect there could be a more elegant solution, like creating a pointer to a version of the function with a and b as fixed values.

Even if it is a really obscure solution, please don't keep it from me, since I feel it could improve my overall understanding of the language.

Answer 1

A viable way of achieving this is to use a struct to store all the values and pass a pointer to that to the function.

struct parameters{
    int valueA;
    int valueB;
};

int function(void* params){
    parameters* data = (parameters*) params;
    return data->valueA + data->valueB; // just an example
}

int main(){
    parameters myData;
    myData.valueA = 4;
    myData.valueB = 2;
    function(&myData);
    return 0;
}