Inline Functions in C: Difference between revisions
[unchecked revision] | [unchecked revision] |
m (Remove from 'Languages' category. Fix 'at least with GCC' position. Change type of include.) |
m (some rewording) |
||
Line 1: | Line 1: | ||
In C you can define inline functions for optimization purposes. |
In C you can define inline functions for optimization purposes. |
||
The problem is that the linker will fail (at least with GCC, with an undefined reference error) if no optimization option (e.g. -O2) is given to the compiler. |
The problem is that the linker will fail (at least with GCC, with an undefined reference error) if no optimization option (e.g. -O2) is given to the compiler. |
||
That is because by default, with no optimization, the compiler doesn't inline functions, and as the compiler doesn't create |
That is because by default, with no optimization, the compiler doesn't inline functions, and as the compiler doesn't create named references or entry points for their separate code, the linker won't find them. |
||
Here is a possible solution that does not require defining the functions twice, and works for every optimization level. This is done by defining them in the header and declaring them as extern inline in the implementation file. |
Here is a possible solution that does not require defining the functions twice, and works for every optimization level. This is done by defining them in the header and declaring them as extern inline in the implementation file. |
||
Line 20: | Line 20: | ||
</source> |
</source> |
||
This way, the compiler inlines the function if possible, but additionally |
This way, the compiler inlines the function if possible, but additionally allocates a name or reference that points to the specific implementation, in case a call is needed when inlining is not possible. |
||
[[Category:C]] |
[[Category:C]] |
Revision as of 16:02, 25 June 2017
In C you can define inline functions for optimization purposes. The problem is that the linker will fail (at least with GCC, with an undefined reference error) if no optimization option (e.g. -O2) is given to the compiler. That is because by default, with no optimization, the compiler doesn't inline functions, and as the compiler doesn't create named references or entry points for their separate code, the linker won't find them. Here is a possible solution that does not require defining the functions twice, and works for every optimization level. This is done by defining them in the header and declaring them as extern inline in the implementation file.
Solution
File: example.h
inline long something(long i)
{
return i + 2;
}
File: example.c
#include "example.h"
extern inline long something(long i);
This way, the compiler inlines the function if possible, but additionally allocates a name or reference that points to the specific implementation, in case a call is needed when inlining is not possible.