Tutorial: Passing a Function, Function callback

Introduction

In this tutorial, we will learn how to pass a mathematical function f(x) as an input argument to another function.

Find derivative of given function

How can you use myfunc() within the function of gradientFunc() that finds the derivative?

• myFun(x): returns F(x)= 2x^3

• gradientFunc(myfunc): returns 6x^2

Example:

void gradientFunc(double myfunc(const double x), double x[ ], double dydx[ ], int m);

Calling a function within another function

There are several methods of calling a function within another function.

Method 1

Calling the function that is defined globally or in the same scope

Download the demo source files

TU_functionCalldemo.cpp

#include "stdio.h"
#include "stdlib.h"
#include "TU_functionCall_header.h"


// These are defined in TU_functionCall_header.h
// double myFunc(const double x);
// void func_call(double xin);

// How to change the function equation in myFunc()
// if myFunc() is defined in library header file?
//
// Q2) What if myFunc2() is needed to be used?
// What do you need to modify in TU_functionCall_header.h ?


void main()
{
	double  xin = 2.5;
	func_call(xin);
}

TU_functionCall_header.h

#pragma once

#include "stdio.h"
#include "stdlib.h"

double myFunc(const double x) {
	double y = x * x;
	return y;
}

double myFunc2(const double x) {
	double y = x * x * x;
	return y;
}

void func_call(double xin)
{
	double y = myFunc(xin);
	printf("Y_out = %f \n", y);
}

Method 2 (recommended)

Pass a function as an input argument to another function.

Download source files

TU_functionCalldemo2.cpp

#include "stdio.h"
#include "stdlib.h"
#include "TU_functionCall_header.h"


// These are defined in TU_functionCall_header.h
// double myFunc(const double x);
// void func_call(double xin);

// Q1) How to change the function equation in myFunc()
// if myFunc() is defined in library header file?
//
// Q2) What if myFunc2() is needed to be used?
 
// ANS: pass the function as an input argument for a higher flexibility

double myFunc(const double x) {
	double y = x * x;
	return y;
}

double myFunc2(const double x) {
	double y = x * x * x;
	return y;
}

void main()
{
	double  xin = 2.0;
	func_call(myFunc, xin);
	func_call(myFunc2, xin);
}

TU_functionCall_header.h

#pragma once

#include "stdio.h"
#include "stdlib.h"



void func_call(double func(const double x), double xin)
{
	double y = func(xin);
	printf("Y_out = %f \n", y);
}

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