At what stage of compilation inline function is replaced with fn call & in what conditions inline function will fail?

Question

I have few queries about inline function, can anyone please help?

1. In what stage of compilation inline function is replaced with function call?
2. Under what conditions inline function will fail?
3. How to verify whether inline function is successfully replaced or not?

Answer 1

Inline functions are not always important, but it is good to understand them. The basic idea is to save time at a cost in space. Inline functions are a lot like a placeholder. Once you define an inline function, using the 'inline' keyword, whenever you call that function the compiler will replace the function call with the actual code from the function.

A WORD OF WARNING: Inline functions are very good for saving time, but if you use them too often or with large functions you will have a tremendously large program. Sometimes large programs are actually less efficient, and therefore they will run more slowly than before. Inline functions are best for small functions that are called often.

Finally, note that the compiler may choose, in its infinite wisdom, to ignore your attempt to inline a function. So if you do make a mistake and inline a monster fifty-line function that gets called thousands of times, the compiler may ignore you.

Comments

Thank you,
I know it is on compiler whether to consider our inline request or to ignore it,
What i am asking is, there are some conditions, as you said if function is very long, or lets say if it is a recursion function then it will fail, Right?
So i am asking is for which other conditions it will fail? Can you help?

Answer 2

Most of the things are cleared by SiddalingKumar - Just adding few points
1. How to verify whether inline function is successfully replaced or not?
This substitution is performed by the C++ compiler at compile time. When the compiler inline-expands a function call, the function's code gets inserted into the caller's code stream (conceptually similar to what happens with a #define macro)

Point no 2 has been discussed by SiddalingKumar in detail, the only thing which I want to add is most compilers do automatically inline functions, it's best to declare inline just to describe intent.

Point no 3. No idea...

Comments

Thank you Sir,
Generally in pre-processor stage of compilation macro and header file will be included, So, to Check whether inline function also gets replaced in pre-processor stage or not, I have compiled a CPP code with '-E' option and created a file with '.i'
And i found that it is not replaced. in pre-processor stage.
Please note that function was only 1 line code and very very simple code

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Inline function is not pre-processor (precompilation) processing. Its at the compile time.