How to declare and use inline functions in C language?

In C language, the inline keyword can be used to declare an inline function. Inline functions automatically insert the function’s code directly at the location where it is called during compilation, instead of executing it through a function call.

To declare an inline function, you need to add the keyword “inline” before the function definition. For example:

inline int add(int a, int b) {
    return a + b;
}

Then you can use inline functions just like regular functions by calling them.

int result = add(2, 3);

It is important to note that inline functions should generally be defined in header files for use in multiple source files.

Moreover, the compiler may decide whether or not to actually inline expand functions based on its own optimization strategy, so it cannot guarantee that all function calls will be inlined. You can use the compiler’s optimization options to specify the behavior of inlining functions, such as using the -O3 option to enable the highest level of optimization.