I have a class for storing the position of an object in 2d, and I have to do some checking before a value is assign to the X and Y.
Should the "checkRange()" function be inline?
Code:class Position { public: Position(int nx, int ny); void setPos(int nx, int ny); private: int x,y; }; void Point::setPos(int nx, int ny) { x = nx; checkRange(0,50,nx); y = ny; checkRange(0,100,ny); } void checkRange(int min, int max, int &value) { if(value > max) value = max; if(value < min) value = min; }
The compiler will decide on its own if it should be inlined or not. Typically, when working with modern compilers, they automatically inline functions if it's advantageous.
Ubuntu Desktop
GCC/G++
Geany (for quick projects)
Anjuta (for larger things)
I've always wondered why the inline keyword exists, since compilers can inline without it and they can refuse to inline even if you specify inline?
Does specifying a function as inline make it more likely that the compiler will actually inline it?
So does that mean the compiler will inline if and only if you suggest it as a inlinable candidate?
Example:
Code:inline void someObj::someFunc(){ // May be inlined if compiler agrees to it? return; } void someObj::anotherFunc(){ // Will never be inlined because of no explicit declaration? return; }
Ubuntu Desktop
GCC/G++
Geany (for quick projects)
Anjuta (for larger things)
No, because "if and only if" is a total implication, and we've already established that it is free to not inline a function even when it is declared inline.Originally Posted by dudeomanodude
Declaring a function "inline" causes the linker to ignore multiple definition errors. That's pretty dang important.
Compilers are/were generally designed to compile each source file separately. With this practice, it is impossible for a compiler to inline a function that written in a different source file. The solution: have potential inline candidates be included in header files. The problem with that is multiple definition errors. So the inline key word was invented to allow multiple definitions for functions intended to be inlined.
People say that gcc is smart about figuring out which functions to inline, as far as I can tell, it cannot possibly inline a function unless a) it is declared inline, and included in a header, or b) it is declared in the source file unit that it is used in. Basically it boils down to a gcc can't inline a function call if the function being called is not included in the same compilation unit.
It is too clear and so it is hard to see.
A dunce once searched for fire with a lighted lantern.
Had he known what fire was,
He could have cooked his rice much sooner.
There are, of course, further optimizations. I don't know if it applies to inline, but the linker can also perform optimizations on code after the compiler. These optimizations are at least available in Visual Studio.
You might need to specify a high enough level of optimisation, or specify the particular optimisation that causes good candidates to be automatically inlined, or use the inline keyword to suggest suitable candidates to the compiler.The compiler will decide on its own if it should be inlined or not. Typically, when working with modern compilers, they automatically inline functions if it's advantageous.
In this case it probably is a suitable candidate to be inlined, but if the compiler disagrees, it will not inline it anyway.
Look up a C++ Reference and learn How To Ask Questions The Smart Way
No. For example, g++ with the -O3 option or -finline-functions option will inline functions that it considers good candidates for inlining, even if they have not been declared as inline. If they have been declared as inline, then they might be inlined at a lower level of optimisation.So does that mean the compiler will inline if and only if you suggest it as a inlinable candidate?
Look up a C++ Reference and learn How To Ask Questions The Smart Way
When you profile your code, does this function appear to be a bottleneck?
Not at all, but thought that that function should be inline so I wanted to ask. I never used the inline keyword before.When you profile your code, does this function appear to be a bottleneck?
So if you are using a good compiler, dont bother with inlining?
Don't bother with premature optimization. If your code is slow, profile it. Then fix what is slowing it down.
A profiler is a bad way to find inlining candidates. Inlined code can trigger a cascade of optimizations which completely change the profile, not just a few particular timings.
Some functions, frankly, are braindead obvious for inlining. The one originally mentioned by the OP is a borderline case. I would not personally inline it, at least initially, but I wouldn't view it as a premature optimization, either.
Don't prematurely inline.
If you don't know that you need to, then you shouldn't do it.
My homepage
Advice: Take only as directed - If symptoms persist, please see your debugger
Linus Torvalds: "But it clearly is the only right way. The fact that everybody else does it some other way only means that they are wrong"
