In the previous chapters, we have read about both the topics of pointers as well as the functions in C++. But in this chapter, we are going to learn how these two concepts can be used with one another in C++. Both these topics are of utmost importance and are really fun to use. So let us take a look at them in detail.
Passing pointers to functions:
C++ allows the coder to pass a pointer to a function. To do so, simply declare the function parameter as a pointer type.
#include <iostream.h>
#include <ctime.h>
void gS(unsigned long *par); //function declaration
int main () {
unsigned long sec;
gS( &sec );
// print the actual value
cout << "Number of seconds :" << sec << endl;
return 0;
}
void gS(unsigned long *par) { //function definition
// get the current number of seconds
*par = time( NULL );
}When the above code is compiled and executed, it produces the following result −
Number of seconds: 1294450In the above example, we pass an unsigned long pointer to a function and change the value inside the function which reflects back in the calling function.
Return Pointers from Functions:
C++ also allows the feature to return pointers from the functions. For this purpose, we use the following
Syntax:
int *Func_name() {
.
.
.
}Note: Here we are returning an integer value because, pointers are actually addresses, which are actually numbers themselves.
#include <iostream.h>
#include <ctime.h>
// function to generate and retrun random numbers.
int * getRandom( ) {
static int r[5];
// set the seed
srand( (unsigned)time( NULL ) );
for (int i = 0; i < 5; ++i) {
r[i] = rand();
cout << r[i] << endl;
}
return r;
}
// main function to call above defined function.
int main () {
// a pointer to an int.
int *p;
p = getRandom();
for ( int i = 0; i < 5; i++ ) {
cout << "*(p + " << i << ") : ";
cout << *(p + i) << endl;
}
return 0;
}Output:
672723198
9998735695
804513585
971235677
618989504
*(p + 0): 672723198
*(p + 1): 9998735695
*(p + 2): 804513585
*(p + 3): 971235677
*(p + 4): 618989504
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