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Passing pointers to functions in C++
C++ 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 <iostream>
#include <ctime>
using namespace std;
void getSeconds(unsigned long *par);
int main ()
{
unsigned long sec;
getSeconds( &sec );
// print the actual value
cout << "Number of seconds :" << sec << endl;
return 0;
}
void getSeconds(unsigned long *par)
{
// get the current number of seconds
*par = time( NULL );
return;
}
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When the above code is compiled and executed, it produces following result:
Number of seconds :1294450468
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The function which can accept a pointer, can also accept an array as shown in the following example:
#include <iostream>
using namespace std;
// 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
cout << "Average value is: " << avg << endl;
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;
}
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When the above code is compiled together and executed, it produces following result:
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