inline vs __inline vs __inline__ vs __forceinline?
What are the differences between these four inline (key)words?
inline
, __inline
, __inline__
, __forceinline
.
inline
is the keyword, in C++ and C99.
__inline
is a vendor-specific keyword (e.g. MSVC) for inline function in C, since C89 doesn't have it.
__inline__
is similar to __inline
but is from another set of compilers.
__forceinline
is another vendor-specific (mainly MSVC) keyword, which will apply more force to inline the function than the __inline
hint (e.g. inline even if it result in worse code).
There's also __attribute__((always_inline))
in GCC and clang.
__inline
, __inline__
and __forceinline
are all implementation specific. Because of the double underscore they are all identifiers reserved for the implementation so shouldn't conflict with identifiers used in applications.
inline
is the only C++ keyword.
For the Visual Studio compiler it means:
inline - suggestion to the compiler to inline your code
__forceinline - overrides the builtin compiler optimization and generates inline code
For more details see: http://msdn.microsoft.com/en-us/library/z8y1yy88%28VS.71%29.aspx
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