The __inline keyword suggests to the compiler that it compiles a C or C++ function inline, if it is sensible to do so.

The semantics of __inline are exactly the same as those of the inline keyword. However, inline is not available in C90.

__inline is a storage class qualifier. It does not affect the type of a function.

__inline int f(int x)
{
    return x*5+1;
}
int g(int x, int y)
{
    return f(x) + f(y);
}