What Exactly is a Free Function in C ?

Understanding the Concept of "Free Function" in C

Encountering the term "free function" within the boost::test documentation often sparks questions about its precise meaning. Initial assumptions might suggest that a free function is one that lacks a return value, implying a void return type. However, further exploration reveals that free functions also seemingly exclude arguments.

To clarify these notions, let's define what a free function truly represents in the context of C programming:

In C , a free function is simply a function that exists outside of any class or structure. Unlike member functions, which belong to specific classes and have access to their data members and methods, free functions operate independently.

Every function in C that doesn't exhibit membership to a class or structure is considered a free function. This categorization includes functions that don't return any values (void return type) and functions that do accept arguments.

Here's an illustrative example:

struct X {
    void f() {}       // not a free function
};
void g() {}           // free function
int h(int, int) { return 1; } // also a free function

In this example, the function f defined within the structure X is not a free function because it belongs to the X structure. On the other hand, both g and h are free functions since they aren't associated with any class or structure.

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