Function pointers

FUNCTION POINTERS

C programming language allows you to pass a pointer to a function. To do so, simply declare the function parameter as a pointer type.

Following a simple example where we pass an unsigned long pointer to a function and change the value inside the function which reflects back in the calling function:

#include <stdio.h> #include <time.h>

void getSeconds(unsigned long *par); int main ()

{

unsigned long sec; getSeconds( &sec );

/* print the actual value */ printf("Number of seconds: %ld\n", sec ); return 0;

}

void getSeconds(unsigned long *par)

{

/* get the current number of seconds */ *par = time( NULL );

return;

}

When the above code is compiled and executed, it produces the following result:Number of

seconds :     1294450468

The function, which can accept a pointer, can also accept an array as shown in the following example:

#include <stdio.h>

/* function declaration */

double getAverage(int *arr, int size); int main ()

{

/* an int array with 5 elements */

int balance[5] = {1000, 2, 3, 17, 50}; double avg;

/* pass pointer to the array as an argument */ avg = getAverage( balance, 5 ) ;

/* output the returned value */ printf("Average value is: %f\n", avg );

return 0;

}

double getAverage(int *arr, int size)

{

int i, sum = 0; double avg;

for (i = 0; i < size; ++i)

{

sum += arr[i];

}

avg = (double)sum / size; return avg;

}

When the above code is compiled together and executed, it produces the following result:

Average value is: 214.40000