Where Should Default Parameter Values Be Defined in C ?

Defining Default Parameter Values in C

In C , where should you define the default value for a function parameter: in the declaration only, in the definition only, or in both places?

The answer is that the default parameter value must be specified in the declaration, not in the definition. The declaration is the only visible part of the function to the caller, so it must contain all the information necessary for the function to be called correctly.

In other words, the default parameter value is part of the function's type signature. It determines the type of the parameter and whether it has a default value. If the default parameter value is omitted from the declaration, the compiler will assume that the parameter does not have a default value and will generate an error if it is not provided by the caller.

For example, the following function declaration defines a function that takes two integer parameters, x and y, with default values of 0 and 1, respectively:

int foo(int x = 0, int y = 1);

The following function call invokes the foo function with the default values for both parameters:

int result = foo();

The following function call invokes the foo function with a non-default value for the x parameter:

int result = foo(5);

Note that the default parameter value for y is still used in the second function call, even though the x parameter is explicitly specified. This is because the default parameter value is part of the function's type signature, and it is not possible to override it in the function call.

It is possible to define the default parameter value in the function definition, but this is not recommended. The definition is only visible to the compiler, and it does not affect the function's type signature. As a result, it can be confusing to maintain, and it can lead to errors if the default parameter value is changed in the declaration but not in the definition.

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