Where Should Default Parameter Values Be Placed in C Function Declarations?

Default Parameter Value Placement in C

In C , you can specify default values for function parameters. The placement of these default values has important implications for how the function is called and used.

Default Parameter Value Placement in Function Definition or Declaration

The question arises, where should the default parameter value be placed: in the function definition, declaration, or both places?

Answer:

Default parameter values must appear on the declaration. This is because the declaration is the only part of the function that the caller sees. When a function is called, the caller provides the arguments that will be passed to the function. If a parameter has a default value, the caller may choose to omit that argument, in which case the default value will be used.

Definition Example:

int function(int x, int y = 5);

In this example, the default value for parameter y is defined in the function declaration and is set to 5.

Edit:

It is important to note that while it is possible to have the argument on the definition, it is recommended to write code as if that is not true. By placing the default parameter value in the declaration, you ensure that the caller is always aware of the default value and can make an informed decision about whether to provide an explicit argument or use the default.

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