The use of "inline" keyword in C

In C, the inline keyword is used to request the compiler to replace the function call with the function code itself (similar to a macro), rather than jumping to the function's memory location. This can sometimes speed up your program by saving the overhead of a function call. However, it's merely a suggestion to the compiler, and it might choose to ignore it.

Benefits:

1. It can make the code faster by eliminating the overhead of a function call.
2. It prevents multiple function call overheads if used inside a loop.

Downsides:

1. It can make the compiled code larger, since the function code is duplicated every place the function is called.
2. Not guaranteed to be inlined. Compiler can ignore the suggestion.

Example:

Consider the following C code:

In the above example:

• The square function is a regular function. When it's called, the program will jump to its memory location, execute the code, and then return to the calling location.
• The inline_square function is declared as inline, suggesting the compiler replace calls to it with the actual code of the function. This means that, instead of jumping to another memory location, the code return x * x; would be placed directly where the function is called.

Remember, the keyword inline is only a suggestion to the compiler. The compiler is free to ignore this suggestion and treat the function like a regular function, especially if the function is large or complex. If inlining is crucial, you might want to look into using macros (with caution, since they have their own pitfalls).