Pass by Reference vs. Value in C : What's the Difference and When Should I Use Which?

Passing by Reference vs. Value in C

When passing arguments to functions in C , there are two primary methods: passing by value and passing by reference. Understanding the distinctions between these two approaches is crucial for effective coding.

Pass by Value

In pass by value, a copy of the argument is created within the function's scope. This copy has its own reference, distinct from the original argument. Therefore, modifying the local variable within the function has no impact on the original object outside the function.

Pass by Reference

Pass by reference, on the other hand, grants the function direct access to the original object. However, different interpretations of this term exist:

Argument vs. Parameter Reference

Some individuals refer to pass by reference as passing the object being referenced, not the argument itself. This is different from pass by value, where a new object is created within the function.

Mutability of the Object

Others claim that pass by reference implies the object cannot be modified within the callee. In this view, a function that modifies the object's value affects it both within and outside the function's scope.

Definition of Pass by Reference

To clarify the confusion, let us define pass by reference as follows:

An argument is passed by reference if and only if the corresponding parameter has a reference type and binds directly to the argument expression. In all other cases, it is pass by value.

Examples of Pass by Reference vs. Value

Consider the following examples:

• Pass by value:

  • void f1(Object o);
  • f1(Object());
  • Passing a literal value, such as int i = 42;

• Pass by reference:

  • void f1(Object *&op);
  • Object a; Object *op1 = &a; f1(op1);
  • Passing an object directly by reference, such as f2(b)

Implications of Pass by Reference and Value

• Modifications to objects passed by reference persist beyond the function's scope.
• Modifications to objects passed by value do not impact their original values.
• Pass by reference is more efficient in passing large objects, as it avoids copying.
• Pass by value guarantees object integrity if the function may inadvertently modify the object.

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