Lab Exercise 13: Function Pointers

# Objective

This demo provides a working example of function pointers in action. Function pointers are not frequently used in C programming (perhaps due to their strange syntax), but can be extremely useful in some circumstances.

## Software Tools

Installation
Instructions
Windows Linux Mac OSX
MPLAB® X
Integrated Development Environment
MPLAB® XC16
C Compiler

## Exercise Files

Installation
Instructions
Windows Linux Mac OSX
Project and Source Files

# Procedure

1

### Open the Project

Start MPLAB® X IDE, then click on the Open Project icon on the main toolbar

Navigate to the folder where you saved the exercise files for this class.

Click on the Lab13.X folder.
Select Open Project .

2

### Debug Project

Click on the Debug Project button. This will build and send the program to the simulator.
Click on the Continue button. This begins the simulation.Wait for the UART1 Output Window to finish outputting.
Click on the Halt button. This will stop execution so that we may examine the results.

3

### What just happened?

As was done earlier in the class, we opened a pre-configured MPLAB® workspace with a complete, working program. We then compiled the code and ran it long enough for it to complete its task. This program uses a function pointer to pass the address of a mathematical function to another function that will compute its integral.

The integral example was adapted from one published on Wikipedia at: http://en.wikipedia.org/wiki/Function_pointer. The integral function takes three parameters: the upper and lower bounds of the integral, and the address of the function that it is to evaluate. The function’s header looks like:

float integral(float a, float b, float (*f)(float))

Note that the third parameter is defined as a function pointer. When we call this function, we only need to provide the name of the function we want to integrate. For example:

y2 = integral(0, 1, xsquared);

The function xsquared() is a simple mathematical function defined as:

float xsquared(float x)
{
return (x * x);
}

There are other functions that may be passed to the integral() function as well.

# Results

4

### End Debug Session

Clear the UART 1 Window - put the cursor in the UART 1 Window then enter Ctrl +L. This will clear the UART 1 Window before your next simulation.
End the Simulation Session by clicking the Finish Debugger Session button.

Then CLOSE the Project by right clicking on Lab02 from the Projects Window and then selecting Close.

# Conclusions

Function pointers, while not frequently used, can provide a very convenient mechanism for passing a function to another function.
Many other possible applications exist

• Jump tables
• Accommodating multiple calling conventions
• Callback functions (used in Windows™)
• Call different versions of a function under different circumstances