Pass By Value
This method uses in-mode semantics. Changes made to formal parameters do not get transmitted back to the caller. Any modifications to the formal parameter variable inside the called function or method affect only the separate storage location and will not be reflected in the actual parameter in the calling environment. This method is also called call by value.
Example of Pass by Value
The below example demonstrates pass by value in function.
C
// C program to illustrate// call by value#include <stdio.h>void func(int a, int b){ a += b; printf("In func, a = %d b = %d\n", a, b);}int main(void){ int x = 5, y = 7; // Passing parameters func(x, y); printf("In main, x = %d y = %d\n", x, y); return 0;} |
In func, a = 12 b = 7 In main, x = 5 y = 7
Shortcomings of Pass By Value:
- Inefficiency in storage allocation
- For objects and arrays, the copy semantics are costly
Note: Languages like C, C++, and Java support this type of parameter passing. Java in fact is strictly call by value.
C doesn’t support call by reference.
Parameter Passing Techniques in C
In C, there are different ways in which parameter data can be passed into and out of methods and functions. Let us assume that a function B() is called from another function A(). In this case, A is called the “caller function” and B is called the “called function or callee function”. Also, the arguments which A sends to B are called actual arguments and the parameters of B are called formal arguments.
Terminology
- Formal Parameter: A variable and its type as it appears in the prototype of the function or method.
- Actual Parameter: The variable or expression corresponding to a formal parameter that appears in the function or method call in the calling environment.
- Modes:
- IN: Passes info from caller to the callee.
- OUT: Callee writes values in the caller.
- IN/OUT: The caller tells the callee the value of the variable, which the callee may update.