Where Should Default Parameter Values Be Specified in C ?

Default Parameter Values in C : Where to Specify Them

Wondering where to specify default parameter values in C ? Unlike some other languages, C enforces a specific placement rule to ensure consistency and clarity.

Declaration vs. Definition

The answer lies in the difference between function declaration and function definition.

• Declaration: The part that lays out the function's signature (name, return type, parameters).
• Definition: The actual implementation of the function body.

Rule:

Default parameter values must be specified in the declaration of the function. This is because the caller interacts with the function through its declaration, not its definition.

Example:

// Declaration with default value
int foo(int x, int y = 5);

// Definition without default value (optional)
int foo(int x, int y) { /* ... */ }

In this example, the default value of y is set in the declaration. This is required because the caller needs to know what the default value is in order to decide whether or not to pass an argument for y.

Additional Considerations:

• While it is technically possible to specify default values in the definition, it is not recommended. Such code may not be as portable and could lead to confusion or errors.
• In older versions of C , default arguments could only be declared in header files, but this restriction has been removed in modern versions.
• Default values should be constant expressions, as they are evaluated at compile-time.

The above is the detailed content of Where Should Default Parameter Values Be Specified in C ?. For more information, please follow other related articles on the PHP Chinese website!