减少C中函数的参数数量

Question

I want to do a numerical integration of a function f using the qtrap function defined in "Numerical recipes in C".

double qtrap(double (*func)(double), double a, double b);

As shown, it is a 1-d integration of a variable of type double.

But the function I want to integrate has an additional parameter a:

double f(double x, int a)
{
    return a + x * x;
}

Now I am looking for a way to integrate f for different values of a.

My idea up to now:

typedef double (*fctp1_t)(double);       //function pointer type for 1 arg
typedef double (*fctp2_t)(double, int);  //function pointer type for 2 args

int a = 10;
fctp1_t = f1d;
f1d = reduceArgument(f, a);

qtrap(f1d, 0, 1);

with the reduceArgument something like this:

fctp1_t reduceArgument(fctp2_t f2d, int ia)
{
    return f2d(x, ia);
}    

This code results in the error: 'x' undeclared.

Thanks for any suggestions.

Answer 1

C does not allow to build a function like that. You have two way to solve your problem:

• modify qtrap so that it is able to handle a parametrized function;

• use a global variable to pass the parameter implicitly.