When should I write the keyword 'inline' for a function/method?

Question

When should I write the keyword inline for a function/method in C++?

After seeing some answers, some related questions:

• When should I <

Answer 1

• When will the the compiler not know when to make a function/method 'inline'?

This depends on the compiler used. Do not blindly trust that nowadays compilers know better then humans how to inline and you should never use it for performance reasons, because it's linkage directive rather than optimization hint. While I agree that ideologically are these arguments correct encountering reality might be a different thing.

After reading multiple threads around I tried out of curiosity the effects of inline on the code I'm just working and the results were that I got measurable speedup for GCC and no speed up for Intel compiler.

(More detail: math simulations with few critical functions defined outside class, GCC 4.6.3 (g++ -O3), ICC 13.1.0 (icpc -O3); adding inline to critical points caused +6% speedup with GCC code).

So if you qualify GCC 4.6 as a modern compiler the result is that inline directive still matters if you write CPU intensive tasks and know where exactly is the bottleneck.