Call by Reference

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Definition

Passing actual address of variables from the caller funtion to the function definition is called as call by reference or passing by reference.

Description

• Here '&' ampersand symbol is used before the argument in caller function to pass actual address location number of the argument and at function definition '*' operator symbol is used as a pointer to access the value of the argument.
• Change in the value of variables in definition function will affect the value of variables from were you passed in.

swap(&a,&b);   //caller function with actual arguments
.
.
.
swap(int *x, int *y)   //function definition with formal arguments
{
//function body
}

When to use

When there is need to change the values of variables in the calling function or program.

Source code

Output

Original values of a:1, b:2
Swaped values in swap function a:2,b:1
After swaping the values of a:2, b:1

Program working steps

• First 2 lines are preprocessor directives which include defintion of functions like clrscr(), printf() etc.
• Void main function, from where the program execution starts.
• Declaration of two variables a and b with integer data-type.
• clrscr() fucntion to clear the screen like cls in windows and clear in linux.
• Printing of original values a and b before swapping.
• swap(&a,&b); caller function with two arguments passes address location number of the value using '&' ampersand operator.
• By invoking the swap caller function the program control transfers to line no.13.
• swap function definition contains two arguments declared with integer pointer x and y. The address(reference) which is passed from the caller function is stored in these two pointer variables x and y.
• Variable temp is used for temporary storage to swap the values of x and y.
• Line no.15 int temp = *x; statement assigns the value stored at location address specified in *x into the variable temp. In the same way next two statement are evaluated by the compiler.
• Swaped values of a and b in swap function are then printed and program control is transfered back to main function using return 0; statement.
• After returning back to main function swap values of a and b are printed once again.
• getch() function to wait for user to exit from the program.
• From output of the program you can learn that when you modify the values using pass by reference to a function, then there is also change in the value of the variables from the calling function.

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