Understanding Default Parameters in C and C : A Comprehensive Guide

Congratulations on stating something simple in the most confusing way possible. The concept of default parameters in C and C can indeed be clarified without resorting to convoluted explanations. Let's break it down into a digestible and clear guide.

What Are Default Parameters?

Default parameters in C and C are a feature that allows you to provide default values for function arguments. If a caller does not supply a value for a particular argument, the function uses the default value instead. This can be particularly useful for making functions more flexible and reducing the number of overloaded function signatures needed.

For example, if you have a function like this:

int myFunction(int a, int b  10) {    return a   b;}

In this case, if the second argument is not provided in a function call, the default value of 10 is used.

Compiling and Linking in C and C

It's important to understand how compilation and linking work in C and C . Every C/C source file (.cpp) is compiled separately into an object file, and the linker then combines these object files to create the final executable. The compiler does not know the address of any global or static variables or functions within other files. This is the job of the linker.

When a function call is made during the compilation process, the compiler generates code to push the parameters onto the stack and include a CALL instruction. However, the compiler does not know the address of the function being called; this is the linker's job.

For the compiler to know how to call a function, it needs a declaration that specifies the parameter types. This is why default parameters must be declared. If a parameter is not specified in the function call, the compiler has no way of knowing the value, hence the need for a declaration.

Function Definitions and Declarations

Function definitions and declarations are distinct, but they can be used together to specify default parameters. Here's an example:

int countVocals(char *s, bool countDiphtonguesAsOne  false);

This is a declaration that includes a default parameter for the second argument. The corresponding function definition could look like this:

int countVocals(char *s, bool countDiphtonguesAsOne) {    // Function implementation}

If the first statement is a header file, it serves as the declaration and can include default parameters. If the function definition is in the same file, it can omit the declaration, but the definition must have default values. Alternatively, a "dummy" declaration with default parameters can precede the definition.

Non-Member Functions and Overloading

No, non-member functions can indeed have separate declarations. Here is an example of a non-member function declaration and definition:

int countVocals(char *s, bool countDiphtonguesAsOne  false); // Declaration
int countVocals(char *s, bool countDiphtonguesAsOne) { // Definition
    ...
}

It is also important to note that functions that do not appear in a class can be inside a possibly nested namespace. Functions in a namespace do not need to be declared as global.

To summarize, understanding default parameters and function declarations in C and C is crucial for writing clear and efficient code. By using the right combination of declarations and definitions, you can ensure that your code is both easy to read and compiles without errors.