I've come across the following signature
double(&rotate_vec(double(&val)[4]))[4];
In the comments it "claims" to accept and return an array of four elements. My first reaction was that this does not even look standard c++ yet this compiles:
double(&rotate_vec(double(&val)[4]))[4] { // ... return val; } int main() { double ar[4] = { 1, 2, 3, 5 }; rotate_vec(ar); return 0; }
- How is this c++ ? How would you read it ?
- We can't return an array from a function, just pointers, or can we ?
With C++03 the best you can do to simplify the original
double(&rotate_vec(double(&val)[4]))[4];
is to use a typedef, to wit:
typedef double Four_vec[4]; Four_vec& rotate_vec( Four_vec& val );
In C++11 you can write
auto rotate_vec( double (&val)[4] ) -> double (&)[4];
although I'd use a typedef or C++11 using to clarify.
Regarding
“We can't return an array from a function, just pointers, or can we ?”
you can't return a raw array by value, but you can return a pointer or reference, or you can wrap it in a struct, like C++11 std::array.
double ( &rotate_vec( double (&val)[4] ) )[4]
A function named rotate_vec
double ( &rotate_vec( double (&val)[4] ) )[4]
...that takes as an argument, a reference to an array of four doubles
double ( &rotate_vec( double (&val)[4] ) )[4]
...and returns a reference to an array of four doubles.
