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; } 

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 <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; } 

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

 Average value is: 214.4