why are inline keyword in header c++

Explanation of the inline Keyword in C++

The inline keyword in C++ is used to suggest to the compiler that it should attempt to perform inline expansion of the function. This means that the compiler will replace the function call with the actual code of the function, which can potentially improve performance by reducing the overhead of function calls.

When to Use inline Keyword: - The inline keyword should be used when the function is small and frequently called, as it can potentially improve performance by reducing the overhead of function calls [8].

Considerations for Using inline Keyword: - It's important to note that the decision to inline a function is ultimately up to the compiler, and using the inline keyword is just a suggestion. The compiler may choose not to inline the function if it deems it inappropriate [8].

Member Functions and Function Templates: - Member functions defined in-class are inline by default. Function templates, including member functions of class templates, are normally defined in headers and therefore inline [8].

Best Practices: - It's recommended not to put an inline function in what is meant to be a stable interface unless you are certain that it will not change. An inline function is part of the ABI. Additionally, constexpr implies inline [8].

Static and inline Functions: - There are occasions when you want to use static in header files. However, static prevents you from declaring local functions in a header file. This is a good thing, as it's recommended to prototype local functions in the module that they appear [5].

In summary, the inline keyword in C++ is used to suggest to the compiler that it should attempt to perform inline expansion of the function, potentially improving performance by reducing the overhead of function calls. It's important to consider the size and frequency of function calls when deciding to use the inline keyword, and to be aware that the decision to inline a function ultimately lies with the compiler.